1. Person who constantly stays up cleaning, washing, organizing, powertooling, sorting or otherwise keeping themself busy doing menial tasks.
2. Someone who constantly makes slight alterations on (usually a very specific) object, i.e. computer, software, automobile, etc.
3. A compulsive liar, thief, or both.
4. A methamphetamine ("tweak"), or other form of speed, addict (who displays all of the above in an obsessive-compulsive manner).
"I've been real busy sorting bolts!"
"For three days?"
"It's important though..."
What's the difference between a crackhead and a tweaker?
The crackhead will steal your shit and bounce--the tweaker will steal your shit and then help you look for it.