From McWSweeney's, presented without further ado, here are some bar jokes involving grammar and punctuation by Eric K. Auld:

1. A comma splice walks into a bar, it has a drink and then leaves.

2. A dangling modifier walks into a bar. After finishing a drink, the bartender asks it to leave.

3. A question mark walks into a bar?

4. Two quotation marks “walk into” a bar.

Three more over at McSweeney's: Link

Challenge: Can you come up with more?