Thomas Shey
Legend
I'll take the wikipedia definition: letter of the law without the spirit, in order to gain advantage. Especially since rules lawyers rarely bring up rules that would be detrimental to them.
I have to note this depends on the game culture they worked under. I've played with groups that some people would call horrible rules lawyers, but we were also extremely insistent on making sure it applied when it didn't work for us, to.
Honestly, people will only argue them when its to their benefit are, at best, not any good at looking at the game as a whole, and at their worst just selfish. Rules are just their method of expressing that, but its not really about the rules for them.
(Its possible to think that the rules as written are undesirably punitive to PCs, but there's a time and place for that discussion; if you only wait for it to bite you to complain (at least after the first time when you simply may not know it well enough) there's a problem.)