How can I kill all processes for a user in Linux?

In Unix, I often would type "killall". This would immediately kill all proccesses (including simple login shells) except for the one I ran killall in. This was great when I knew a user had logged out completely and had tons of left over processes or crashed programs... I could su - to be him, and run "killall". This was particularly handy at the end of the day, when I didn't need my 20 open windows anymore.

In Redhat, killall seems to work very differently, and nothing in the man pages for kill or killall suggests a solution.

Oh wise Linux world, please help!

maybe something like:
kill -9 `ps -aef | grep username | awk '{ print $2 }'`