This is one of my favorite questions to be asked...
I've been wanting to field test "I'm an amateur gravedigger" just to see how they respond...however, i don't expect it to play all that much haha
Jay Wa has a sticky with a few really good ones. You can find them all here:
the-best-tease-routines-by-jay-wa-vt18584.html
I would just respond with something rediculous. Although if you want it to go off the lines of being an eye doctor, I would say something like "I treat the windows to people's souls"
There are probably more creative ones that people will share...