Someone didn't pull it out in time.
Is there a dog?
H Edit: I don't like explaining jokes but since the first guy didn't get I might as well: When pronounced in a French accent it sounds like ash.
Al Kaline.
Oily!
Pull the pin and throw it back
Parents
Failure to pull out in time
Someone that didn't take it out in time.
In each scenario, there's a dumb guy who didn't take it out in time.
You can unscrew a lightbulb.