"#Aurora is trending, clearly about our Kim K [Kardashian] inspired #Aurora dress ;)" CelebBoutique posted on Twitter several hours after 12 people were killed and more than 50 injured in an Aurora, Colo., movie theater during a midnight screening of "The Dark Knight Rises."
"Well, here's your worst tweet of the day," Fox News Channel commentator Andy Levy posted on Twitter.
"Holy Mother of God are you kidding me?" Twitter user E.J. Maroun of Indiana posted.
"Way to kill your business with one tweet," posted "VegasTommy" among a barrage of incredulous messages flooding the microblogging service.
"Trending" is short for "a trending topic," a word, phrase or topic cited, or tagged, on Twitter at a greater rate than other words. Twitter says trending topics are intended to help Twitter and their users understand what is happening in the world.
CelebBoutique -- an online firm that does not say on its Web site where it is based but has a postal address in Buenos Aires -- posted an apology on Twitter and Facebook later Friday.
"We are incredibly sorry for our tweet about Aurora," the firm posted on Twitter.
"Our PR is NOT U.S. based and had not checked the reason for the trend, at that time our social media was totally UNAWARE of the situation and simply thought it was another trending topic," the post said.
"We have removed the very insensitive tweet and will of course take more care in future to look into what we say in our tweets. Again we do apologise for any offense caused this was not intentional & will not occur again. Our most sincere apologies for both the tweet and situation. -- CB"
It later posted a slightly more formal apology on Facebook, adding it hoped "the families of the victims will accept our greatest sympathies and apologies along with the American public."
The firm did not immediately respond to a United Press International e-mail asking, among other questions, if the social-media firm was still working for CelebBoutique.
The Kardashian Aurora dress did not appear on the CelebBoutique Web site when UPI checked Saturday afternoon.
The CelebBoutique Web site says, under job vacancies, it is looking for "United States PR," the UPI check indicated.