The invitation sets the tone for a party and gives the guests clues about what to expect. Of course, when you're writing an invitation, politeness is important, especially since you want the people who receive your invitation to actually attend your party. Writing an invitation that is meant to exclude certain people can be tricky but it is possible.
Open with a tease. Begin your invitation by flattering your guests. Let them know that they were carefully chosen to attend your party and that you didn't just send invitations to everyone you know.
Include everyone else. Instead of excluding people from your party, let the invitation state who's included. The message will get across that no one other than these people are welcome. "Ladies, let's get together and party," tells guests their husbands and boyfriends are excluded from the festivities.
Be funny. Use humor in your invitation to express your intentions. Something like "This murder mystery party is not for the squeamish, so leave your children home" lets people know that children are excluded from the party, but it does so in a way that won't offend anyone.
Say it right out. Sometimes the nature of the party requires strict attendance guidelines to make the party a success. It may be important that only couples attend your party, like in the case of a swingers party. When it is important, state it right on the invitation: "Couples only."
Make guests want to conform. If you don't want to come right out and state your exclusions in the invitation, you can word the invitation in such a way that anyone who doesn't fit your target guest list would be uncomfortable attending the party. For a football party, list some party activities: "Come cheer on the Miami Dolphins, compete with fantasy football picks, and toss the old pigskin at half-time." With those activities on the agenda, the non-football-fans you wish to exclude from this party won't attend.