Abbreviations are sometimes used for players as well. This might add a bit of confusion, but most of us are just too lazy to type full names. I'll list a few here.

FS: Firesword
DS: Darkshadow
JJT: JJ Tublear
NS: Newspaz
TS: Turtleslayer
ST: Steeltalon
SSJ: Super Saiyan (mind you, i have seen people with SSJ in their name online. they aren't the same person)
UR: Unknown Rabbit
CB: Craccoboy
FQ: Fquist (added by request *hiss*)
MB: Messageboard Megabyte Moonblaze

Most other player name abbreviations still contain enough letters to indentify the person. I probably forgot tons of others, but this list should include the ones you'll encounter most frequently.