Young Sheldon emphasizes how badly Sheldon's friends handled his more negative tendencies in The Big Bang Theory. Known for his eccentricities on top of his high intellect, the socially inept genius can be demeaning and mean at times, even to the people he's closest with. Despite this, the Pasadena gang had been mostly understanding of him but, it turns out, that's not the best way to react to some of his most unreasonable demands.
Ever since Sheldon was introduced in The Big Bang Theory, he's been quite difficult to be around. That's why at one point, Penny was wondering how he's even able to make friends with Leonard, Howard, and Raj. As it turns out, it was all a coincidence. During this time, Penny hadn't noticed that she, too, had been accommodating Sheldon's requests. To make matters worse, she was also typically the subject of some of his rudest comments; aside from making fun of her lack of academic achievements, he also humiliated her for her relationship choices despite him not having anything to do with it. Mostly, this made for some cheap laughs, but as seen in Young Sheldon, this was ultimately detrimental to Sheldon't overall arc.
Following a minor car accident with Meemaw, Sheldon was traumatized over the experience, so much so that he was too scared to ride in another vehicle in Young Sheldon season 4, episode 13, "The Geezer Bus and a New Model for Education." Because of this, he opted to skip going to school altogether, but in his attempt to not miss any classes, he asked Dr. Linkletter if he could give him a personal session over the phone. The professor initially said no, but Sheldon escalated the issue to the East Texas Tech President Hagemeyer who was more than willing to accommodate his request. Knowing full well how important the young genius is to the school, the college executive went above and beyond in helping their star student; she obliged when he requested a second phone line and even sent strawberry Quick and Star Trek videos to his house to make him comfortable. When Mary found out about this, she was frustrated, asking Hagemeyer to stop because she wants "Sheldon to function in a society and it does not help if you give him everything that he asks for," — something that his The Big Bang Theory friends also needed to hear.
Sheldon's Big Bang Theory friends tolerated his behavior because he's not intentionally being mean; instead, he was just being himself, in his own unique way. This made it so much easier for Sheldon to take advantage of them, as he felt entitled to be coddled or obliged by his friends as seen more explicitly in the earlier seasons of The Big Bang Theory. The very existence of the Roommate Agreement, in which the included rules and regulations were mostly intended for Sheldon's own benefit, was proof of this. Every single time Leonard would justifiably be mad at him or refuse to do something for him, Sheldon would cite the Roommate Agreement to get what he wanted. Aside from Leonard, Penny was also often a victim of Sheldon's bullying given that she lived across the hall. While Sheldon got some push back for his most ridiculous requests, his friends ultimately obliged; because of this, they failed to force him to learn that he's not the center of the universe. This effectively made it more difficult for Sheldon to work with other people outside of his group because the majority of the public wouldn't tolerate his behavior.
Towards the end of The Big Bang Theory, Sheldon somehow mellowed down, becoming more sensitive to other people's feelings. This was after Amy started being more active in reminding her partner to be empathetic towards, not to mention respectful of, their lives. Sheldon still had some tendencies as seen in his outburst in the finale after winning a Nobel Prize, but for the most part, he's better overall. But if only his friends listened to Mary's principle in Young Sheldon, his progress towards becoming a better person may have gone quicker.