[FrostKiwi]

Huh, I swear I heard in a positive context before. But English in not my native language, so my feel on the nuance of this expression is probably a bit off.

[johtso]

There's a subtle distinction. "Like ... on crack/steroids" means a really good / fast version of something (I think steroids is probably the more common variation) e.g. "an e-bike is like a bicycle on crack". "They're on crack" means "They are crazy".

[l33t7332273]

I’ve heard “on crack” used similarly to “on steroids,” as an American English speaker.

For example, it would not be out of the question to say something like “when the iPhone launched it was amazing. Like a palm pilot on crack.”

So, when used positively, “on crack” is generally a modifier(in my experience). When used alone it does seem to have negative connotations.

[furyofantares]

I think it's used like that for products rather than humans. "X is like Y on crack."