I'd say in a pitch, unless you're really good (judging from your question you're not quite there yet, and few people ever are) situational humor is OK, while all other humor should probably be cut completely. If something funny happens during the pitch, it's ok to joke about it. Planned humor usually doesn't go over well.

We had a phrase or two in our pitch (not the slides, but verbal communication) that were a bit humorous, and it happened to work really well. But it's very easy to overdo it, and ultimately, it's unlikely to make much difference.