hand 1: he was short stacked, the board could have easily missed you, he took a stab at the pot, and when you reraised him he only had to call 7 to win 21. Also, he could also have 3 outs to a jack because you could be pushing lower pocket pairs at this point too. Not a bad play on his part, nor your, thats just how the cards fell.

hand 2: by checking AK in the BB, you are asking for a random 2 pair to be hit on you and you can't put your opponents on a range of hands.

hand 3: I probally fold this preflop. But if you do call you have to push this flop with your stack...

hand 4: villien decides to donk some chips off to you and gets lucky