To have sex with a friend or acquaintance's mother; Usually as part of a single, ill-advised, drunken episode. Sometimes resulting in unplanned pregnancy.

Origin: rumors that James Doohan (actor of Star Trek fame) commonly had sexual intercourse with the mothers of his Star Trek castmates (crew).

Mostly used within the phrase "pulling a Doohan"

A person with an incredibly small, and usually bent penis, often a "Doohan" will try to make up for this with fast cars or big muscles.