Another story from games past. Back in college I was running a small campaign over the summer with some of my friends. Things were going fine we were several dozen games in. The party ran afoul of a stone golem at one point. The party went to town hacking away at it. I said nothing and recorded damage like normal. I would write most of the damage in black pen and a few hits in red pen. After the damage totals were well over 200 hitpoints the players started going WTF is going on.
For those of you that don't know stone golems are one of the rare monsters that require a magic weapon to deal damage to, normal swords hit it but just don't do it any harm. After a few minutes of trying to figure it out the players suddenly realized what was going on. Most of them had a magic weapon that wasn't optimal for them so they switched. One player who didn't have anything then said, "Man I'd suck a dick for a plus 1 sword right now" This phrase has become a catch phrase for anytime the players really feel like they are getting screwed by the game rules in my game.