Were you intentionally playing trappy or cautious? as you mention just flatting him in position with AK as well. Depending on how much he was opening and from what positions both of these hands can easily be 3bet for value and put extra pressure on the opponent at this late stage, after all you have him covered and have position so you should be bossing him not the other way round. I understand the tactic of flatting with big hands behind, especially if this guy is a bit splashy with his chips but 3 betting might help you simplfy subsequent decisions as it will help define his range a bit better. 

As above the hand in question is read dependent. It’s a pretty ugly spot but I think he is just trying to put pressure on a lot of the time and not giving up that easy. His line is similar to a line I take at times if someone is constantly flatting the BTN against me and just stabbing when checked to. This line is dependent on board texture as well. I find it a good tactic for protecting my OOP checking range on the flop, but it sounds like this guy might be abusing the tactic somewhat so I dont mind your response (as long as you thought it through and didn’t do it out of spite).