Every group need at least one person who can quote the steps for grappling or tripping without having to look it up every time. However, recently I had to do some rule lawyering because it would have a) caused the death of the entire party along with half a city block and b) I believed the DM was wrong in doing so. Basically, I had to make a case that there was no way that everyone on the board was going to take 100d6 of damage from an explosion. Eventually, I talked him down to 25d6 and reduced the radius of the blast. Later on, I looked up the rules on the said explosion and it turns out that he was about 10d6 over, but the radius of the blast was about right. My problem was that the DM was willing to kill the entire party for no good reason and also give a mundane item some serious power. Normally, I let the rules bend, stretch, and disappear altogether if need be, but this one time, I just couldn't see a barrel of gunpowder being so powerful. Rule lawyering can be annoying, but sometimes it needs to be done to save the party.
Go Fast, take Chances, and for Tier's sake, Don't Wear a Helmet!