The Clown Murders (1976)

Four buddies at the polo club decide they haven't done a good caper in awhile.  So they decide that it would be a great joke to grab Alison, the wife of Mr. Sutherland, on the night of the Halloween party.  The couple has plans to sign the paperwork at midnight to close on a house. Not sure why anyone would have a closing at midnight, but there you go.

One of the guys is ordering the costumes for the polo club Halloween party and purposely messes up the costume order.  Everyone ends up with clown costumes. This way it will be impossible to determine who grabbed Alison since everyone at the polo club is dressed like a clown.

While it begins as a prank, it quickly escalates after Mr. Sutherland calls the police and an alert goes out for kidnappers dressed as clowns.  Also the radio report mentions a ransom note, which freaks out the guys since it's a joke not a kidnapping.  All eyes turn to Charlie since he used to date Alison and is the mastermind of the plot. He's not happy that she got married after he'd left to travel for a number of years.

As the group gets in deeper and deeper, they see no way out of this stupid prank.  Relations withint hte group deteriorate and blame starts being thrown around.  Then someone dressed as a clown starts trying to kill them.

This is a depressing, slow, dialogue heavy movie with lots of fat jokes about the overweight guy who's always got a sandwich in his hand.  And no one wants to see John Candy in a serious role that includes a sex scene.