Unexpectedly, they actually had me speak in front of them. The guy running the meeting made up a goofy holiday, and asked me why it was or wasn't a good idea to have it. I then did a quick impromptu speech explaining to the group why it was a good idea to have National Pizza Day. I had fun with it, even though I was totally unprepared.
As comedians, we often rely too much on our prepared material. When a heckler yells something, our material doesn't fly with the audience, or other unexpected things happen, it can be quite disconcerting. In these situations, it is good to come up with something "on the fly". Doing impromptu speeches at places like Toastmasters can help you in these situations.
If you lift weights, you most likely do bench presses. As you know, you need to develop your shoulders and triceps in addition to your chest to make significant gains on the bench press. Think of regular stand up comedy shows as developing your chest, and participating in a Toastmasters meeting as developing your shoulders and triceps. Use this strategy, and you will see significant gains in strength in both your comedy and/or your bodybuilding.
In addition to these benefits, going to a Toastmasters meeting provides excellent networking opportunities. If you attend a lot of local comedy shows, you often will see a lot of the same people there. By going to a Toastmasters meeting, you can tell other members there about your shows and get lots of brand new people to watch you!