Drunk to the point of losing the ability to filter your thoughts. All judgment taken away.
Symptoms involve throwing things, usually wearing a costume (not necessarily Santa), and speaking the truth at high volumes. Lots of pointing.
A straight man in a wedding dress gets up at the bar and points at a stranger. Before he can even get a word out, he realizes that this stranger is a man he once met three years ago and always wanted to tell him he's a loser because he's fat. At top volume, the santa clause drunkard points at the man and tells him he's a fat loser.
Then the drunk decides to chug his drink and proceeds to throw his glass at the owner of the bar who is in fact a female. Now the santa clause drunkard is severely and/or possibly tasered.
That's when you know someone is santa clause drunk.