Is it safe?
Funny that you should say that. I once used that gag on a dentist. He had a VERY negative reaction. I think he may have heard it before and didn't quite appreciate being compared to Der Veis Angle. Not sure on that spelling.
I've since retired that bit from my act.
Also, this is no joke. My current dentist is from Transylvania and he scares me. I will not risk pissing him off. Wait, I lied. I said he scares me. Everybody knows I fear no man.