What are some thresh weaknesses that I can capitalize on in lane as ADC?

long cool downs, a skill shot with a clear wind up on his Q

poke him alot... he has the lowest base armor in game (16) and only gets armor if he gathers souls. so try to harass and poke him if he goes for souls

Although he is a very good champion in the support role there are weaknesses to him. If thresh uses his hook, he is at a disadvantage for 15-20 seconds of its early on, that is your chance to get in range to poke but do not walk up into him because he can flay you. Stay at a distance and poke him and side step. Thresh is very dependent on his abilities because if he misses everything then all he can do is run, as I said just keep a distance, poke him when his abilities are on cd. Your support should be doing the majority of the harassing if they are a ranged support but stick to that above and you should be all good.

When he walks up too far and throw obvious hooks, punish them