A rhyming scheme is a simple way to inject humor into a surprise party invitation. A tongue-in-cheek theme, depending on the type of party, also opens up possibilities for funny invitations.
An easy way to include humor in a surprise party invitation is with a rhyming scheme that incorporates the guest of honor's age. With a little creative thinking, most ages can be paired with a rhyming word: one and fun, thirty and dirty, fifty and nifty, and so on.
The theme of the surprise party also helps set the tone of the invitation. For an adults-only surprise birthday invitation, include a hyperbolic phrase such as "over the hill" or reference alcohol if that is a focus of the party. For a surprise anniversary party invitation, play up the length of the marriage in a humorous way. Referring to a long marriage as a life sentence is one option. For a surprise baby shower, consider a tongue-in-cheek expression such as a "bun in the oven."
Incorporate the surprise aspect of the party into the invitation phrasing as well. One suggested wording from the Invitation Consultants is "Come celebrate one wonderful man / a surprise party is the elaborate plan! / So if he asks, you must tell lies / Spilling the secret would not be wise!"