Noobtuning around corners/over walls when they spot 1 pixel of your hitbox, burst fire is a one shot kill because they only ever need one bullet, shooting out of the SIDE of their barrels because the turn animation isn't tied to their eyes, etc etc etc...
I can swear I've seen some carrying class items, stopping, and switching to weapons not in their class as needed (running into people with rockets after being seen carrying SMGs)
The AI noob tubes really bother me. They shoot them like they're a gun. When watching a replay I saw a bot killing 3 of their teammates and himself with a single grenade launcher round. That simply shouldn't happen. If there's teammates around the enemy that the bot is aiming at, the bot should not use the grenade launcher and should attempt to switch back to rifle mode instead.
Also I am seeing a lack of enemy snipers in coop. It would add another level of challenge to the game that isn't completely random and can be feasibly dealt with. They should take longer to aim than other bots and therefore be more accurate, and should also tend to sit at high, open spots from long range such as second floor in buildings.