Set up (AKA: What you need to know): Husband, Wife, and The Other Man, are all philosophers, and all devout Utilitarians. Husband arrives home early from a business trip, walks in on Wife and The Other Man having sex. It is implied that The Other Man knows the Husband.
Husband: What the fuck is this??!
Wife: It's not what it looks like!
Husband: You're screwing another man! How is this not what it looks like?!
Wife: Well, you were away on a business trip right?!
Husband: You know I was! I wasn't supposed to get back until Thursday, which is why I assume you're having your little fuckfest today!
Wife: Well, I haven't had sex at all since you've been gone! You haven't bothered to do anything at all!
Husband: Because I couldn't! I was all the way in Paris! How the hell am I supposed to have sex with you from that far away?!
Wife: Well, if you were here, would you have sex with me?!
Husband: You know I would! I'd make serious, passionate love to you!
Wife: Well, then I assert that since you would have sex with me, but were unable to, that this man just acted in your Proxy! He did what you would have done, but since you couldn't do it, he did it! It's perfectly in accordance with Utilitarianism!
Husband: Well then. [He Leaves, comes back with a Revolver, shoots The Other Man in the chest.]
Wife: What the hell was that for?! I thought you were a Utilitarian!
Husband: I just acted in proxy of his wife.
A little attempt at some ethics humor. Probably failed miserably, but it made sense to me. First post in OffTopic by the way!!