In his attempt to avoid Adam Loki ended up reaching the ground floor first and therefore also being the first the couple kissing. He froze.

It wasn't like he was unfamiliar with the concept of homosexuality, of course. He'd even gotten somewhat used to seeing two men kiss thanks to his habit of hanging around all sorts of seedy bars back in America. He knew he was supposed to be tolerant. He could be very tolerant in fact, but seeing an angel kissing a demon and that demon in particular was just plain wrong.