Yeah, jokes are difficult, especially when you have to rely on timing. An example of a stutterer who was a comic genius is Rowan Atkinson. He did some non-verbal comedy like the invisible drumset sketch and Mr Bean, but was very funny verbally as well. His stutter was fairly mild and well-controlled. There are episodes of Blackadder with a character called 'Bob', a woman posing as a man who Blackadder fancies. The way he prepares himself to say 'Bob' because it was difficult for him to say makes the whole thing hilarious in the context of the characters' relationship. There are ways to be funny without simply telling jokes.