Contradicting phrases can be really funny. For example, people say,"Since it's cold, close the door and come in."
If you think about it, it doesn't make sense at all. How can you come in when the door is closed?
Some other ones I found funny were
Homemade noodles that were just pulled out of the machine.
Warning, this is the the parking lot. Do not park.
Cold hand warmers.
Mom's hand pie
I know you might not find it funny. Sorry, just don't have anything to do.