Alright, so I'm gonna actually take this as a serious non-QQ thread even though that's what it is. As a former Trundle main (S4), here's what I had the most trouble against:
AP/magic damage
Range
Hard crowd control
High mobility
Basically, Trundle is like Darius in that you shouldn't sit and trade AAs with him. You want to kite and poke around him, or stun him and walk away before he can fight back. If you don't do either of those, you're gonna have a bad time because he's designed to win when you play his game, like most champions. His design is just simpler than most and brutally effective for it.
TL;DR Don't play his game if you can avoid it. If you can't avoid it, minimize losses and look for plays elsewhere.