I was rather surprised to find that "bastard" is a term of endearment.

Fair suck of the sav, Jazzo, mate! I don't reckon that definition's ridgy-didge. A bloke'd wanna be pretty careful who he calls a bastard or he's likely to get in a blue and come a gutser.

On a slightly more serious note, the meaning of the word differs from one extreme to the other, depending on context, intonation and level of acquaintance between the two parties, eg:
"Listen here, you bastard" used in the middle of a heated argument, compared to
"How're you going, you old bastard?" used as a greeting to an old friend.

Hooroo,
Marty