I'm going to tell a funny story at a wedding about the bride
What are you going to say? What is the funny story about?
It's just going to be something fun for the wedding.
There's a thin line between a funny story and one that you shouldn't tell at a wedding, and if you cross that line you could really upset a whole lot of people, but otherwise you should try to have fun. I don't see anything wrong with telling a few jokes at a wedding as long as they're in good spirits and respectful.
I'm going to make fun of my boyfriend by dressing him as a girl while telling the story.
Now I think that crosses the line a bit, is everyone okay with this sort of skit? A wedding is supposed to bring attention to the bride and groom, not you and your boyfriend. How about skipping that for a different event, and just telling your funny story when they ask you to?