The 'Twilight' actor would not ''in a million years'' go on the US comedy programme - which revolves around a number of sketches performed by celebrities - because he would be ''terrible'' at trying to be funny.
He said: ''Doing comedy is impossible. I would be terrible. People have asked me to do things like 'Saturday Night Live', and there is just no way, not in a million years. That's just way too scary.''
The 25-year-old star - who is in a relationship with his 'Twilight Saga' co-star Kristen Stewart - admits he isn't as ''crazy'' as he used to be nowadays because people have certain expectations of him since he became famous.
He added to Reveal magazine: ''I used to not care about what anyone thought about anything. Now I'm forced into thinking about things if I want to have a career. Maybe it's because I'm older.
''I used to be a little bit wilder, but it's difficult to do that now. I used to want to do the craziest things, as I had no understanding that I had an audience. All I wanted to do was weird stuff, but it's different now - people have an expectation. You have to think about things objectively.