My co-workers hate it when I ask this question on a technical interview, but my common one is "what is the difference between a varchar(max) and varchar(8000) when they are both storing 8000 characters"

Answer, you cannot index a varchar(max). A varchar(max) and varchar(8000) both store the data in the table but a max will go to blob storage if it is greater than 8000.

No one ever knows the answer but I like to ask it to see how people think. Then I tell them that no one ever gets that right and it isn't a big deal that they don't know it, as I give them the answer.