This particular rumor isn't half as crazy as Charlie Sheen himself, but it is being reported that The Hangover Part II cast and crew is seeking a cameo from the notoriously bonkers Two and a Half Men star.
Even though The Hangover Part II has wrapped principle photography, director Todd Phillips is rumored to have spent the last couple of days trying to secure Charlie Sheen for an undisclosed role. Earlier in the production process, a Mel Gibson cameo was planned, then axed after unnamed individuals on the crew refused to work with the troubled actor. He was later replaced by Liam Neeson.
If The Hangover Part II is structured like the first film, it is possible that Charlie Sheen will be appearing as himself in the closing credits photomontage. This rumor is expected to be denied by Charlie Sheen and his publicist even if the man does decide to appear.
It is worth noting that the same source for this rumor, Badass Digest, was the source of the earlier The Dark Knight Rises rumor from today, and its possible that the site is trying to drum up some attention with these impossible to verify reports.