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.

[050220 04:56] 0c04c, CK: Jesus Christ...I'm still banned from the messageboard?...

[050220 04:56] 0c04c, CK: I try to check it, first time in fuck all ages, and I'm still banned?...

[050220 04:56] 0c04c, CK: Good goddamn...that's just unhealthy Blakeypoo...