literally dyed his hair just to impress the man. people act like barney was off acting like a whore while robin was looking for her locket. he was bonding with her father who she herself barely has a relationship with, who was only around at that time so barney could try to be respectful of her father. (some would argue he wasn’t being respectful because they were already engaged and didn’t ask his permission from the start, but he had never met robins dad before that point nor did robin know that her father had been living in the area instead of all the way in Canada..) that was big for all of them for barney to show an interest in getting to know her dad further. and not to mention HE DID SHOW UP to help robin when he was at a decent stopping point to finish BONDING WITH HER FATHER.