I've been playing through GTA V again recently and I have to say Trevor certainly had some potential as an interesting character, but overall just ends up becoming the butt of jokes to the point where almost none of his deeper moments can be taken seriously.
One of the best examples of Trevor at his prime, what his character should've been (at least in my opinion) is shown in his conversation with Lamar during Pack Man, and in the starting cut-scene of Fresh Meat with Franklin. In both of these scenes there is a level of reasonable anger and frustration, actual emotion that can be felt within Trevor after Bury the Hatchet, along with a stubborn coldness that can be heard in his tone of voice. He actually gets some real character development and even briefly references himself having a difficult upbringing (even if it is at an odd moment to be brought up). In both of these missions he isn't just crazy for the sake of being crazy, but instead there is an actual cause and reason for him to act out aggressively. It also feels like he's on the verge of losing control but is holding it back, having an internal struggle within himself to fight back against his mental issues (if he actually does have a mental condition).
There was another moment where I switched to Trevor and he was intoxicated, lying on a beach with a drink in his hand, and I kind of felt bad for him as it potentially alluded to his mental issues, depression and alcoholism, but then I was completely taken out of it and my suspension of disbelief ruined as he stood and said some dumb one liner. The whole situation just became a joke and any thoughts I had regarding to the context of Trevor waking up drunk on a beach just disappeared because the game fails to take any of its potential more meaningful moments seriously.
It's just disappointing Trevor ended up so inconsistent. I think it would've been more interesting if Rockstar had of decided to explore the themes surrounding Trevor's mental issues and his struggles with them in a more serious manner instead of having him pull off one liners, randomly flushing body parts down toilets and eating reheated eyeball stew for the sake of lulz. Hell the could've even completely ignored most of Trevor's feelings and made him just a completely morally bankrupt psychopath, but done so in a consistent manner. I guess it represents a larger problem with GTA V overall, as the game does sort of present themes and little bits of social commentary, but never explores any of them very well or just wants to make a joke of it all to the point where nothing of value can be taken away from the experience of the game.