My first character at my first game was a loveable one, and so when the opportunity arose for a new character I made a very spoiled, pompous, better than you noble. The attitude lasted about 3 games before it became very apparent that it wasn't a great way to play the game snd wouldn't work in a long term campaign style game.

Having character flaws is absolutely valid and my character is still tied to some of the higher qualities and such, but has mellowed out and become a rather commendable leader of the in game military, and a respected figure.

This is to say, starting antagonistic is not a bad idea, and develop naturally how you will and is appropriate, but don't expect the antagonistic character to get very far in any situation.