Hi my EnglishForward friends,

US english slang will probably beat the hell out of me...:-). But it's interesting to discover this part of the US english, no kidding. Back to the point, please what does it mean if say to someone that "you were tweaking your ass off" ....I didn't find it at the urbandictionary.com, so it must be very hard slang. I came across to this in this context: FBI agent is questioning someone, who bough an stolen car from some girl:

I'll bet you were tweaking your ass off
and you thought, "Wait, why pay this chick
when I can kill her, take the car and keep the cash?"

Please how would you paraphrase the first part (I'll bet you were tweaking your ass off) ...rest is no problem for me....

thank you in advance...

My guess is, "I'll bet you were using drugs big time!" I'm not sure if "tweaking" refers to a particular sort of drug use, or if it's drugs in general.
After some checking, I think that Avangi's right: visible (to others) drug usage'
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Many thanks guys!!! Your suggestions perfectly fits into the context....Many thanks again...

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My underground source says "crystal meth" (methamphetamines made in illegal meth labs) You can go without sleep indefinitely. Also, as Marius says, exhibiting the signs/symptoms of such use. (I know that's not a sentence.)