(Image Credit: Youtube)

A controversial ad posted at Reebok gyms in Germany has been taken down after it went viral, causing thousands of angry girlfriends to complain.

"Cheat on your girlfriend, not on your workout," the advertisement, which was only posted at Reebok's partner gyms in Germany, said.

The founder of Cheaterville.com, a site that names and shames cheaters, fired off an angry letter to Reebok, calling the ad "disrespectful."

"This form of advertising shows a dishonest and disrespectful attitude towards women and your company should be ashamed to have even placed this ad in various places thinking it would be perceived in any other way," founder James McGibney wrote in a letter obtained by Radar Online.

Reebok said it regretted that some "offensive" materials were printed and stressed that it was not part of a global campaign, CBS Boston reported.

The viral ad was a hot topic on Twitter.

"you kidding me w/ this advertising campaign reebok? what idiot thought it was a good idea??" Reema Patel wrote.

"Damn # reebok …. you pissed off a lot of women!" Share It Fitness tweeted.