I play with an alias as my display name. My character also introduces herself with an alias that's different from the displayed alias. It's just a clear cut case of meta gaming. It makes sense to hide names for characters that might get in trouble for their ethnicity or background. Also makes sense for people that engage in criminal activity to have an alias or a nickname to obfuscate their connections. As the others have mentioned, it's in poor taste to hate somebody over nicknames. Just remember that display names are often used in busier places to get the attention of the player or for easier communication.
