The fake "clitoris" that is all that remains of the penis of a transwoman after "bottom surgery." You know--the one that "not even a gynecologist can distinguish from the real thing" -- unless he looks at it.
The term "learned the clarinet at school" is most commonly used by persons as a way of conveying the fact that they have been known to give fantastic oral sex, particularly on male genitalia.
"I learned the clarinet at school." John said, sending a wink in the direction of his room-mate.