Poker Etiquette

Wanna preface this by saying I was pretty out of it during this game.

Was playing a casual low stakes game with a couple of friends ($15) and one of the guys I play with (Ben) is really big on seeing what other people have, even when they fold. He often shows his cards himself, and will frequently try and grab peoples cards out of the muck to see what they had. Anyways, I wasn’t paying attention and folded after the river thinking I had nothing. Ben won with king high and won the very small pot. As he was grabbing the pot he insisted I show, so I finally did because I had nothing. But when he flipped my cards we realized I actully had a pair of 2s. Laughing, and wanting to teach him a lesson I insisted this made me the winner and took the pot (the other guy backed me, and it was literaly 35 cents.) No one was fussed.

Anyways, fast forward to the end of the night, and I was playing heads up against the other guy for the final hand, and we had a pretty sizeable pot ($10). I had 2 pair, showed, and then the other guy showed and he had the straight. I groaned for a second, but then looked closer and realized that I had actually hit a one card flush on the river (again, I was super out of it, it was a pretty pathetic mistake) but was happy I had won, even if it was pure luck. But as I tried to grab the pot, the other guys declared I had forfeited the pot by thinking I had lost at first. They backed this up by saying I had already made the same mistake earlier. Anyways, it was pretty low stakes but it became a big thing.

Anyways, am I the asshole here? When we showed, I said “2 pair”, saw his straight, groaned, then took a closer look and saw my flush. It all took like 5 seconds. I never declared him the winner, and he never started grabbing the chips. I’ll definitely say the first time was definitely questionable because I mucked, but I just wanted to teach him a lesson about always insisting we show, and it was low stakes. But I really feel for the second time I’m in the right. What’s the usual protocol for something like this. Do I automatically forfeit the pot by declaring the wrong hand?