Mysteriously, "Thanks for the Mammaries" appeared on the message board on my door one day last summer. I can only assume it was written there by one of the guys living there who was used to the house being single-sex as it had been the semester before. I'd always been the number one proponent of going co-ed. This summer I was in charge of renting rooms, and we had 9 Irish girls living there.

Apart from that amount of pure speculation, it's a generally amusing term parodying "Thanks for the Memories," whose author remains unknown.