[Eternal]

Hand 1: Raise a little bigger check fold flop
Hand 2: This is an interesting situation, if you have a history of 3 betting this guy very often you might have to call. But that's very history and read dependent. Otherwise, fold.

Hand 3: I really don't know against an Unknown here. I think you have to call but hate it. But with a person with more 3 betting history/frustration, instacall obv.

Hand 4: everyone's gonna tell u to 4-bet here, but you obviously have your own reasons not to this time. As played you have to call. Your non 4 betting line has probably disguised your hand a bit. This line from CO has to have some kind of history from either you or the "possible" limp squeeze player? With you just flat calling that 3bet, he may see opportunity here.

Or, he was smooth calling trying to trap you.

Either way, you're right that CO's play is a bit weird. I don't think I'll ever play that kind of line with any hand. There has to be a lot of history that we don't know about if he's a regular.