Mariah raised an excellent point in her comments to me, and I wanted to respond.
I am all in favor of students who speak up. I get a huge kick out of the folks who raise the unusual points, or who leap in with a wild guess when no one else is speaking. That makes class more interesting, I hope, for everyone. Hey, I'm human, sometimes I'll have a topic that I've carefully planned out, but the definition and accompanying questions just don't work. Hey, if someone doesn't tell me, I won't know.
It's when a student has obviously not cracked open the textbook in, oh, say, six weeks, not bothered to get the notes for the classes they missed, and expects to be able to jump in... well, then I get annoyed. When the rest of the class gets annoyed with another student, I take that as proof that I'm not truly evil.
Meanwhile, I would just like to report that I have exercised great self-restraint and not eaten all of my Tag-Alongs... yet.