I'm not totally sure, but I don't think it's "an american coloquial expression." That is, it makes sense but I don't think it means anything special. I think it just means that for some reason the high-five was uncomfortable.
Perhaps one person thought it was a good opportunity to high-five and the other person didn't realize, or some other similar situation.
A "high five" is a form of greeting or mutual affirmation in which two people slap the open palm of their (usually right) hands together while extending their arm vertically in a "high" position-- as is so often seen among basketball players after a successful play!
It might come out awkward (torpe) if as Audkaem says one of the those involved was unaware of what the other intended to do or if they almost missed or if one of the two did not feel sufficiently enthusiastic and did it really half-heartedly.