I am pretty sure it was said that it was Paul's friends butt.

I know some people where are from outside the US. Some who have not gotten married yet or been part of a wedding party.

Sometimes the groom has his close friends or family members (like a sister) as a bride's maid. And sometimes the bride has a brother or close friend in the groom's party. It's to balance numbers.

Would it be weird to touch your friends butt (Paul to his friend)? I kinda still think so. Do people do what he claim? I do what he claim, not on the butt, but on the shoulder or in the upper arm, sometimes a room (def in a bar). But not to someone's butt unless I was intimate with them or previously intimate with them.