I am a citizen of France living in Los Angeles (20+ years), I over extended my stay here in the US. I want to go back to France in October for good, but my French (EU) passport expired more than 5 years ago. Should I got the french Consulat and apply for a new one. Am I going to get in trouble from the french authority for letting my passport expired.

You aren't going to be allowed to travel on an expired passport. So you really have no choice but contact the French Embassy or consulate to get it replaced.

You must contact the nearest French consulate to obtain a new passport. Letting the old one expired is not a crime, don't worry. :)