(CNN) Just a word of advice: If you're going to buy one of those band T-shirts from Hot Topic, you might want to do a little research on the band.
Case in point:
Who's Mark Hoppus? Oh, just the bassist and singer for Blink-182, the perennial '90s pop-punk band known for its hit songs like "All the Small Things," "What's My Age Again?" and "I Miss You."
But when the 45-year-old musician tried to compliment his fans on their Blink-182 shirts, they didn't exactly recognize him as the band's front man.
Fans might be forgiven for not knowing what he looks like ... unless, of course, they'd just watched him and the band play the night before at the O2 Arena in London.
But even the morning after seeing the show, one of the guys wearing the band's T-shirts still didn't know who Hoppus was.
Say it ain't so.
Needless to say, the singer and bass player -- and other fans on Twitter -- were not impressed.