Anything that is impossible for me to physically -read- drives me right off the ruddy wall. I hate any and all bookend characters, excessive abuse of the letter X, and numeric references to pot and or simultaneous oral stimulation. But what kills me more than anything else are the people who try and create really dark, brooding names. If your name contains the word "Dark", "Shadow", "Zero", "Lone", or any other teenage-angst-buzzword, please just delete the account now and start over. Your future self will respect you more for it.
And to avoid accusations of hypocrisy, my username on this site is a nickname from high school and is actually pronounced "Fish". Specifically:
"Gh" as in "enough"
"O" as in the plural pronunciation of "Women"
"Ti" as in "Locomotion"
"Ghoti" = "Fish"
Also, at first read it looks like it's trying to say "Goatee", which is the manner of facial hair I had during high school. Not an ideal username, but at least it's grounded in observations of the English language instead of blunt idiocy.