After spending the better part of my youth evading cops and various charges I learned a few things that got me out of more than one tight spot.
The first thing you have to keep in mind is that cops have to take an intelligence test and if they score too high they don't get to be cops so always, ALWAYS, always, treat the cop as a violent, ornery dumbass, the school bully if you would.

First, you must be polite. Their fragile egos are inflated to the point of maximum stretch and the tiniest prick, intentional or not, can make them blow the fuck up. That's why instead "I'm not discussing my night" you should play on their stupidity and bonus points if you can relate to their machismo where they feel sorry for you.
When the cop asks you "Where are you going?" you tell him "I'm just driving around officer."
This is not only an acceptable answer that will keep the pig nice and calm but is also the setup for your excuse.
They will usually ask "What do you mean 'just driving around'?" or something similar and that's when you become best buddies.
"I'm sorry officer, it's just that my girlfriend/wife has been driving me crazy and riding my ass all day and would not get off my back, so I just had to leave before I'm tempted to punch her in the face."
Statistically there's 99% chance that the pig either 1) Has hit a woman. 2) Has thought about hitting a woman. or 3) Has heard other cops talking about hitting women. Either way now you have instantly bonded, you just fed the pig a delicious acorn straight out of your hand.

They said not to lie to the cops but I disagree, lie as long as it's not lies they can catch you on.