Even though he doesn't belong into the main trinity of DC superheroes, the Flash is still a highly popular and capable hero, who's been through a lot. Unlike some other characters, the mantle of the Flash was held by several separate people, not just one.
The most famous reincarnation of the Flash is currently Barry Allen, not only thanks to the comics but also because of the TV show The Flash where he's portrayed by Grant Gustin. Barry also appeared in the DCEU, but he was played by Ezra Miller in the Justice League (2017). The Flash often works with other heroes, and while some respect him, others despise him.
Despises: Kid Flash
Kid Flash also appeared in the TV show The Flash but he and Barry Allen got along just fine in the show since they were adoptive brothers. Barry, of course, later married Iris West, so he became even a more integral part of the West family. However, in comics, their relationship is far more complicated. Wally is the nephew of Iris in the comics and while he admires the Flash, he doesn't particularly like Iris's boyfriend Barry. When Wally gets his powers, Flash begins training him. The relationship between them becomes sour, though, when Wally finds out that Barry is the Flash and that he's been lying to him.
Respects: Avery Ho
As one of the most significant speedsters of the DC universe, the Flash has mentored multiple characters over the years, not just Wally West aka the Kid Flash (see above). Avery Ho is another person he worked with. Avery is a Chinese-American girl who gained her super-speed during a Speed Force storm. Barry Allen helped her master her powers. She briefly joined the China White triad but realized later on that China White had tricked her and turned against her. Avery might not be as known as other DC heroes but that didn't stop her from joining the Chinese version of the Justice League as their Flash.
Despises: Green Arrow
Despite their differences, Oliver Queen and Barry are friends in the Arrowverse. However, they clashed multiple times in the comics, and even though it might be a bit unfair for Oliver to say that he despises Barry, he sometimes considers him naive. Barry works for the police and Oliver is convinced that the police is using its power in the wrong way, a fact to which Barry, according to Oliver, remains oblivious, and that makes Oliver angry at Barry at times. Still, when the need arises, they're capable of fighting together, but the differences in their opinions mean that they might not ever become the best of friends.
Respects: Batman
Gaining Batman's respect is no easy task since the caped crusader is generally skeptical towards anybody else, his fellow superheroes included, but the Flash still managed to get onto the Dark Knight's good grace. Their powers and skill sets are vastly different, which might be the reason why they make such a good team on the battlefield.
The Flash is sometimes nervous when it comes to dealing with Batman, especially when they first meet, but he slowly becomes more confident and the two of them often join forces since they're both important members of the Justice League and fight villains together.
Despises: Green Lantern
Let's switch to Wally West's version of the Flash for a moment. The most famous version of the superhero Green Lantern is definitely Hal Jordan, but the Green Lantern who didn't get along with Wally wasn't Hal, but Kyle Rayner. When Kyle joins the Justice League, he's already an established superhero, but Wally isn't initially so convinced that it was a good idea to allow Kyle to join the League. Wally considers him too inexperienced and unable to follow in Hal Jordan's footsteps. Needless to say that Kyle isn't very fond of Wally either, and the two butt heads more than once.
Respects: Cyborg
The Justice League might not be perfect but one thing is certainly true about this iconic superhero group - they don't discriminate based on someone's age. Some of the Justice League members are older and then there are younger members among them, like Cyborg and the Flash. These two are not the best of friends but they certainly get along well enough, and if they spent more time together in their civil lives as well, they would probably be even friendlier to one another. In the 2017 film Justice League, Victor and Barry struggle to communicate throughout the film, but it doesn't last long, and in the end, they already act like good friends.
Despises: Supergirl
Sometimes it's not the differences in their characters or general distrust but a simple misunderstanding that causes two heroes don't like each other. In Supergirl's case, it was certainly the latter. Supergirl tries to strike a deal with a villain called H'el who promised her that he'd be able to bring back Supergirl's homeworld Krypton.
The Justice League realizes that Kara is being played by H'el and they have to fight her in the process. Kara hates the Flash for stopping her from getting her home back, but once she realizes the truth, she changes her mind and believes the League and Flash.
Respects: Wonder Woman
Wonder Woman is the one superhero who's on friendly terms with most of the Justice League members, and the superheroes she meets in general. So it doesn't really come as a surprise that the Flash and Wonder Woman are friends as well, and Wonder Woman is respectful towards her much younger team member. The Flash is a bit nervous around Wonder Woman at first, just like when it comes to Batman and Superman, but he quickly realizes that Wonder Woman is the last person to be afraid of, and they strike up a friendship. Not only do they get along as people, but they also work well together on the battlefield.
Despises: Jesse Quick
Jesse Quick is a less-known DC superhero who also appeared in the TV show The Flash, where she was the daughter of one version of Harrison Wells. She even briefly dated Wally West but later broke up, more specifically, Jesse broke up with Wally, which he didn't take very well. Their relationship in the show is even more ironic if you consider how their comic book counterparts didn't get along. Jesse originally believed that Wally was training her and helping her to master her powers because he wanted her to be his successor but she later found out that Wally actually wanted Bart Allen to become his successor and was only using Jesse.
Respects: Superman
The Man of Steel is generally a similar case to Diana, at least when it comes to his approach to other heroes. Just like Wonder Woman, unless he's being mind-controlled or otherwise affected, Superman usually does his best to see the good in people, that's what's makes it so easy to get along with him, even if you're grumpy and aloof (Batman, anyone?). Well, the Flash is nothing like Batman and he and Superman make a great team together, even though their competitive streak sometimes shows its ugly head and then they argue about who's faster between them.