I've seen people do a pretty good job playing evil characters who I know to be good people. Quite a long time ago I hosted two games in the Greyhawk, yes quite a long time ago. One was the normal good guys beat up on evil campaign. The other we played just for laughs. They reported to a Dwarf (Dimloin) at his brothel/pub (Dim's Place) on Loin Street. Dimloin was decidedly evil and sold his services to to all manner of evil (High ranking devils and demons come to mind as well as some bad humans). For pure laughs, this was fun. The other campaign was fun too, but in a high stress kind of way.
I definitely experience this. It's fun to play a character much different than your own personality. As mentioned earlier, whats the fun in just playing yourself? My problem is when I try to play an evil or say chaotic neutral character. Most of the time they would appear to be a good character to an outside observer. It's hard for me to have a character commit evil acts.