Mojo Jojo - Evil scientist monkey bad guy in Powerpuff Girls. I chose it as my username on Bebo and it kind of stuck.
Jojo - Because my name is Joanne.
Jo - See above.
Bitchtits - I was doing a thesis on radiation dose to the breasts in certain radiographic examinations (boy that was a fun 6 months) and my friends found this hilarious because I ended up knowing a lot about boobies. One of them called me 'Bitch tits' one day prompting me to almost choke on my cup of tea with laughter. It stuck for a few months but it fizzled out. Thanks be to Jesus.
J-Ho - A dancefloor invention. That Slumdog Millionaire song 'Jai Ho' was popular at the time. This one has stuck.
Yohanne - Mexican guy I worked with couldn't pronounce my name properly. One friend still refers to me as this.