It even happened in FFXI back in the day. Someone would walk up to you, pop open a trade window and throw in a LS pearl hoping you'd accept the trade. That one was always a bit more awkward to me since they are standing literally right next to you lol. Although yes, I do agree that people spamming the invite are annoying; once should be enough to know they are not interested. Maybe they just don't realize they sent you an invite since they are going for everyone. xD