1.To be high on stimulants like Meth or coke.
2.To work obsessively or compulsively on something.
3.To adjust something.
4.To be way wrong about something
1.He did 4 fat ass lines, hes tweakin hard
2.I was tweakin on my room for like 4 hours
3.I was just Tweakin the carb on my truck
4.you think the Boston Celtics are the best team ever..man your tweakin.