Dirty was the first thing that came to Rikku's mind when Mjrn asked her. Of course she knew better to say it out loud, but seriously, how else would you call fighting like her?
"Oh, you know, I like to steal items from enemies, mix items to create bombs and other useful things..." she stopped for a moment. Maybe she meant something different. "O-or do you mean if I prefer fighting monsters or with training partner?"

Perhaps she would make an awkward fool of herself even more, if suddenly a Library Committee member didn't appear.
"You two there! This is a library! How long do you intend to bother other students with your loud discussions?! Do you want to get a detention?!"
Yikes!
"Oopsie... Mjrn, I think we'd better run!"