Why Did Conor McGregor Punch This Older Fellow In The Head At A Bar???

Apparently, Conor McGregor punched this older gentleman in the head due to a whiskey dispute. I've had Conor's whiskey and I thought it was pretty good but maybe he turned a shot, down? Not sure if he insulted Conor or he was pissed because of something else but I can't justify this even as a fan.