Just a silly crossword-type cryptic clue. 9 letters.
This isn't a full answer, but just some pieces that might help lead to a collaborative solution.
The last part of the clue, "in three directions", makes me think of
compass directions -- N, E, S or W. Specifically, three of those four letters in some order. And the "in" part makes me think something else is going to be inserted into the middle of them -- e.g., EN______W or N______ES.
As for "can't stop twitching", perhaps
"twitching" signifies an anagram? In which case, we would want some six-letter word or phrase for "can't stop" that could be inserted into the blanks above.
And that would leave "Bum" as
the literal definition.
If bum means
and can't stop twitching is
a sideeffect of taking steroids
what can be found in
three directions, because directions is an anagram of STEROID NIC
Then we have
ass and steroid
which can be "twitched" to
Another clue could be
bum means "travel, with no particular purpose or destination" Doesnt that fit good to asteroids?
And the answer is...:
bum = anal, twitch = tic, can't stop twitching = tics, three directions = y-shaped, can't stop twitching in three directions = y-tics, anal + y-tics = bum can't stop twitching in three directions!