Hey how can I sound like this guy who's doing the male parts (riff raff)?

Don't, you'll just wind up with a sore throat. If this song is at least in your range, then try to interpret it your own way. You can sing it in a different accent, or try to sound spooky or mysterious, or just sing it the way you normally sound. This song is from a "rock" musical, so it's generally sung in a rock 'n' roll style, but if you wanted to sound downright "operatic"--who's to say you can't?

Different actors put their own twist on the part.

This is from the1975 movie:

http://www.youtube.com/watch?v=sg-vgGuTD8A

This is Glee:

http://www.youtube.com/watch?v=jEpJastNeVE

Rocky Horror 40th Anniversary Tour:

http://www.youtube.com/watch?v=phLmf1PhB6Q

Rocky Horror Picture Universal Orlando Show:

http://www.youtube.com/watch?v=VOUCW265lnY

Rocky Horror Flashmob (Liverpool):

http://www.youtube.com/watch?v=KKugercPzHc