Me and my coworker at McDonald's are friends and we have a special handshake that involves some kind of hug. We did it at the of today's shift and all of a sudden the managers start accusing us of sexual harassment. I want to know if that's true.
If both of you are fine with it, it's not sexual harassment. It would be if one of you felt harassed by it.
I would talk to your managers and try to find out why it is a problem for them. Maybe they find it inappropriate at work? Maybe they feel threatened in some way? I can imagine someone is afraid you try to hug them too, and in this case it should be enough to just explain them you are doing it with your friend because you are friends, but would never do it with someone who doesn't want to be hugged.
Edit: As cdkMoose pointed out, depending on how the hug was there is a chance it was sexual harassment. In that case it would be a good idea to talk to the managers, and try to find out why they percieved it as such.