Putting together a list of the best cinematic badasses is easy. There's Dirty Harry, Mad Max, Ripley and John McClane to name just a few. These are characters that know how to handle themselves and, more importantly, how to look cool doing it. Part of the innate appeal of cinema is watching larger than life characters overcome impossible odds, while doing things their own way. People like Clint Eastwood make it all look effortless yet there are plenty of examples of actors trying - and failing - to make the leap into badass territory.
They may lack the grit needed to make it believable, or they might not have the right body type to convincingly pull it off. In some cases it might be that they were cast based on star appeal instead of their ability to play the part, with the final product suffering as a result. One thing's for sure; when this happens it's pretty distracting.
Watching an actor attempt to play a tough character and failing miserably simply makes for an uncomfortable viewing experience. If the movie depends on the audience buying that the character is super awesome and can win any battle, then they had better come across that way onscreen.