|Dunno, maybe bears...|
And this one self-referencing hipsters:
|Hipsters... no wait, hamsters|
There's something more to the joke format that I'm beginning to find wearing, though, and I think it's the Conventional Set-up --> Twist format. Even though this is essentially how jokes work, it has somehow become a cliche on blackboard coffee shop signs.
I was at the annual meeting of the Linguistics Association of Great Britain last week. I go every year, as I'm on the committee, and it's held in a university somewhere in the UK. They had this sign: