Well, if you want to get into such things.  How about the time a student
raised his hand--during a discussion of disclaimers in contract law--and
earnestly asked, "What do you do if one comes to your door?"  Then there's
"ammendment," and "fudiciary" (you know, the fudiciary duty), and "wether"
for "whether."  This one always gets a laugh when I tell the students that a
"wether" is a castrated goat (hence the term "bellwether," as wethers--I
used to have one--are very docile and tame and come when they're called).  I
suppose the thing that gripes my cookies as much as any is when students
misspell a word that is on the page they're working from.  Some learn,
however, and that makes it tolerable.