Here's the truth: celebrities don't owe us anything. Just because we see a celebrity out in the world doesn't mean that they owe us a selfie, an Instagram shout-out, or even a smile. You would think a fellow celebrity might understand this, but that's not always the case. Charlie Sheen still has beef with Rihanna for not taking a photo with his then-fiancée Brett Rossi, and he spewed the grossest comments on Watch What Happens Live to prove it. In 2014, Sheen took Rossi out to dinner at a Santa Monica restaurant where RiRi was also eating. When Sheen requested that Rihanna meet Rossi, the "Work" singer declined. The former Two and a Half Men star then went on a Twitter tirade against the pop star, insulting her outfit and insisting that they were better off not having met her at all. Umm, okay. After Sheen made the comments, Rihanna clapped back on Twitter telling Sheen to get his "diapers out of a bunch." Now, the TV star has gotten the last word years after the fact. When Watch What Happens Live host Andy Cohen asked Sheen if he made up with Rihanna, the actor pretended not to know who Rihanna was, then responded: "Rihanna... Oh! That bitch!" Yikes. Craig Robinson, who was sitting next to Sheen on the talk show, looked appalled. Twitter immediately reacted to Sheen's insult: