This is one of my pet peeves. At a party once, this girl claimed to be a fellow Iron Maiden fan. When I spoke with her, however, she had only heard one song; the rerelease of Run To The Hills and she didn't know anything about the band at all.
It really bugged me; all she had to do was say "I only know one song, but I'd love to hear more" and that would be fine. But instead she felt she had to tell lies. I also, back in the day, met a girl at Glastonbury '98 who claimed to be a big Manic Street Preachers fan. She was also lying; she'd only heard Design for life. Why must people feel they have to tell lies like that? They'll only get found out once they meet a real fan.