Though the LEO entries don't seem very complete, or at least, not well marked, which may explain part of the confusion.
I think 'tick off' in the sense of 'ausschimpfen' is only BE (AE would be, for instance, 'chew out'), and 'tick off' in the sense of 'verärgern' is probably AE, at least chiefly.
And 'tick off' in the sense of 'abhaken' is definitely only BE, because Haken in the sense of a pencil mark is always 'check' in AE, 'tick' in BE, so the verb in AE is also, unsurprisingly, 'check off.'
And IMO it's not slang, just colloquial language.
If we could get a few more corroborating comments on all these, particularly the first two, I would be willing to make a Wrong Entry thread to suggest the corrections.