Afternoon class moment:
Student: "Is that a tripod?"
Ms. Green: "It's an easel."
Student: "An easel? Isn't that one of those furry little things that runs through the woods?"
Ms. Green: "ummmm...that's a 'weasel'"
OK, I'm pretty sure he was just being a wiseass, but it's hard to tell sometimes, and I know you're not supposed to laugh at students, etc., but I just couldn't help cracking up.
In Piers Anthony's Xanth novels, wasn't it the Demoness Metria who was always using the wrong words?
Ms. Green: "<...>, why aren't you doing your pseudocode?"
Student: "I can't, Ms. Green, I'm in a ditch!"
<pause>
Ms. Green: "Do you mean a 'rut'?"
Student: "Yeah, that's it, a rut."
Ms. Green: "OK—"
Student: "But a rut isn't big enough hold the amount of stuckness I have..."
Ms. Green: "So you needed a ditch."
Student: "ExACTly."
Fortunately, it only took a few minutes to get him out of his ditch...er...large rut.