The respective properties within Marvel and DC have crossed paths several times in the past, but never has there been a crossover that paired Wally West's Flash with Peter Parker's Spider-Man. Believe it or not, the two never so much as shared a panel together in the few times that Marvel has crossed over into DC territory. What makes this so surprising is because The Flash and Spider-Man are such similar characters that it would feel like a no-brainer to pair them up in some capacity.
Of course, a speedster's powers couldn't be further from being different from that of a web-slinging wall-crawler, but it's their personalities that ring off as so similar to each other. Though Flash does have a form of Spider-Sense, the heroes are otherwise very different. Both are too cocky for their own good to the point of arrogance and can't help but quip their villains to death in the middle of any battle, regardless of how high the stakes are. Both heroes have been accused by both characters in-universe and critics of not taking their respective situations seriously enough when appropriate, but in Wally West's philosophy at least, that's the whole point.
Wally explains his philosophy in Justice League: Road to Dark Crisis #1 during the "Life of Purpose" portion of the comic by Jeremy Adams, Rosi Kämpe, and Matt Herms. During a battle against Giganta alongside Kid Flash, Wally can't help but do his usual quips, leaving his sidekick scratching his head on how he could make time for "dad jokes" at such a time. This leads into an inner monologue from Wally where The Flash explains he jokes so often as a way to remain a beacon of light within the Justice League. Given the Justice League's recent deaths in the road to Dark Crisis, this is more important than ever. To give people around him some minor relief from a world full of pain and to remind himself of why he does what he does, The Flash commits to being "the 'hope' guy." That sounds like a philosophy that Spider-Man should be able to relate to himself.
Wally's monologue really puts the cocky hero trope into an entirely new perspective. Heroes like The Flash and Spidey aren't cocky for the sake of cockiness, but to brighten up a dark day. Quips are what keep Spider-Man from killing his villains. At the very least, to be the beacon of hope for the hopeless. It's easy to forget just how important a brief moment of joy could be on a dark day, but Spider-Man and The Flash are happy to be that reminder for bystanders.
Knowing that the two share such a complex but uplifting philosophy is even more reason why they need to cross over into each other's worlds at some point. Besides just opening the doors to tremendous chemistry between Spider-Man and The Flash, it would just be fun to see two heroes with similar outlooks exchange quips against a common enemy. Spider-Man has teamed up with a handful of DC characters like Superman while The Flash has had his own Marvel encounters, but the two are long overdue to share a crossover together.
Look for Justice League: Road to Dark Crisis #1 available now from DC Comics!