A giant erection. Derived from the slang phrase, "to pitch a tent"; however, it is know that people named Malcolm (Malcolm X, Malcolm in the Middle, Dr Malcolm, etc.) all create large tents.
Onlooker: Whoa!! That's a huge erection!!
Malcolm Lastname: Ya, I pitched a malcolmtent eh? Bet you're jealous!
Onlooker: I sure am!! It's like a... ...circus tent!!