A person who is not only proud to be liberal, but represents everything the far-right seem to be against, especially if you are non-white, non-christian, gay/lesbian, or a combination of all of those, or you associate with them.
"Liberal bastard" may sound like a degrading term, but it's not. Basicly it means you're proud to be open-minded and don't give a shit about what others may think.
Bigot: Stupid fags are the cause of everything wrong with America.
Liberal Bastard: Gee thanks I'm gay
Bigot: I bet you're some nigga too
Liberal Bastard: Acutally no
Bigot: Ok then
Liberal Bastard: But my boyfriend is