Because 7 ate 9.
or
Three skunks fighting over a pickle
First dog: My master calls me Furball. How about you?
Second Dog: My master calls me Sitboy
or
Because she wanted to get a good scoop.
or
The barman says "Sorry we don't serve food in here"
or
Nice belt!
or
I said, "I've been on telly but I'm no Dean Martin".
or