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.

[050719 16:34] 8b403, Peanut: as you can see... i should never be allowed near a computer while drunk...

[050719 19:32] 96ea8, *Beniah: Nope...he hits on me...constantly.

[050721 03:04] 5dbf8, *Topaz: woot! remembered my password...

[050721 03:05] 5dbf8, *Topaz: woot! remembered my password...

[050721 03:52] deb0b, *Daisetsu : ...

[050721 03:54] deb0b, *Daisetsu : ...

[050721 03:56] 6edf8, Peanut: ...wow, someone's here...