And we thought the Brits appreciated a little raunchiness.
Now British media watchdog Ofcom is investigating the complaints, according to the BBC.
So what was the big deal?
To tell the truth, we're not really sure.
Aguilera was clad in a barely there black number while grinding out "Express" on a chair. Rihanna, meanwhile, ripped off a striped overcoat to reveal a bra-like top and some undies during a rendition of "What's My Name."
In other words, it's nothing we haven't seen before. But with 17.2 million viewers watching this show, Ofcom (similar to the FCC in the states) is determining whether the singers and producers (including Cowell) broke a boradcasting code that protects children from viewing inappropriate shows too early in the evening.
So far Team Cowell doesn't seem to be sweating. "We are confident that the performances given by our guest artists were appropriate for the show," says a show spokeswoman.
By the way, some dude named Matt Cardle won the show. In case you care.