Five: One to change the bulb and four to pull the ladder out from under him/her.
or
Well, first let's talk about the concept behind this whole "light bulb" thing.
or
I've been framed!
or
Answer: The back of his head.
or
Two. One to take out the bulb and drop it, and the other to try and sell it before it crashes.
or
It's not a shrub, it's a lemon tree my dear Watson.
or