Keywords are inclusive, so the more keywords you put in, the less lines you'll find.
You can specifically ask for a keyword to not exist by prefixing it with !.
For example, searching for "mouse !cheese milk" would find lines that contain both mouse and milk but not cheese.

[050518 15:21] 1fc7a, Peanut: test

[050518 17:45] 1fc7a, Peanut: tenst

[050522 17:05] 4f15e, Vaticus: Just wondering if anyone has any links pertaining to RPG chat rooms. A couple buddies of mine are looking for some.