Can a funny message still work for a wedding?
Yes for the friend group, carefully for everyone else. Many couples send one clean, warm version to the mixed list and let the jokier version live in the group chats. If only one message goes out, put the joke after the facts so the invitation reads as sincere first and funny second.
What if people think the party itself is a joke?
Anchor the humour to concrete facts immediately: a real venue name, a real time, a reply deadline. The page behind the link settles it in one tap, which is the difference between an inside joke and an invitation that reads like one.
Is there a length limit on funny?
The joke should survive being read at speed on a bad connection. Three sentences before the facts is a comedy routine; one is an invitation. If it needs a paragraph, split the bit and the details between the message and the page.
Do forwarded messages reach guests I did not invite?
They can, which is a thing the wording cannot control but the reply form can. Answers come back only inside the plus-one limits you set, so a curious forward sees the party without booking a seat at it.
Funny or polite for a dinner party?
It depends who is laughing. At a table of friends who have eaten your cooking before, funny is just honesty with rhythm. At a table mixing bosses, in-laws and neighbours, politeness travels further. There are samples of both on the polite invitation page.