In the spirit of this thread, I once did (what I think was) an awesome shtick, and I'm still proud of it until today (perhaps wrongly, but still...).
I came to Aisle 9 in Lakewood, and a car was parked across two spots. Normally, when a car is taking up two spots, you can't know if it's really their fault, as maybe the cars that came before parked funny, and this was the only option at the time. But at Aisle 9, there are medal rods at the end, so it was obvious that this person could've moved into the last spot. (see below, red car was offender, green car was mine. I also attached a Google picture, which shows a car parked there properly.)
So... I just blocked the car in, and went inside to do my shopping. Sure enough, a few minutes later a lady comes in and starts calling out, "who's blocking my car?!" I calmly told her that it's me, and that she was only entitled to one spot, and that the other spot was rightfully mine, and I was therefore justified to take the only other available spot, which incidentally blocked her in. She was very not happy, but I softly said that I was almost done my shopping, and I would be happy to move my car as soon as I finished paying for my stuff.
I'm quiet certain that she thought twice the next time before parking selfishly again.