The worst one I've pulled off was back when email was new, and people where naive.
I discovered that you could, using a little knowhow, make an email that seemed to be from anyone.
I sent an email from
john.arbuckle@yale.edu offering a friend a football scholarship.
It took him 3 hours to realize it was a april fools joke... (ended up calling his dad & everything)
(note the name, recognize it?)
God damn, it was funny, but also soooo evil.