Students were playing skill building games on the computer...filling in holes like fractions, integer operations, etc.  Things were getting loud.

Me: HEY!  If you guys can't stay on task, we can't do things like this anymore.
Student: But we were on task!
Me: I'm sorry, arguing with the person next to you over who gets to name their character "Sexy beast" isn't "on task".
Student: That was only at the beginning, COME ON!