A liquid moustache -Similar to a Milkstache- developed while drinking rum(Or other alcohols) from a wide rimmed container like a glass. Can burn or leave rashes if left unchecked for long enough as the alcohol harms the sensitive upper lip skin. Sometimes enjoyable to have a member of the opposite sex lick off.
James woke up with a bad rash after failing to wipe off his rumstache
My girlfriend had a big rumstache after her swig, so I used it as a reason to lock lips.