I have two, Jonny & Long-neck. Because I'm tall. Some nicknames of other people I know are man-tits, no bollocks and gas leak. No bollocks got his name from when we used to play Counterstrike and his voice was so high he sounded like a girl.
Man-tits is probably self explanatory.
Gas leak is the name we give to someone who says "Sad" all the time, but he really draws out the S so it's more like "Ssssssssssssssssssssssssaaaaad". During an airsoft nightgame I did an impression of him doing this and managed a good half minute with just the S and no bollocks thought that one of our handguns had a gas leak, and it just stuck.