Straight up, implies honest and direct, unless it's a drink in which case it would be undiluted. A straight-laced person is conventional and respectable.
I had my hair straightened today. What do you think? Does it make me look straight-laced? Should I change it straight away?
Here's a competition which doesn't require you to keep your characters on the straight and narrow. There's a £1,000 first prize so I'm going to get straight on it. And here's a Valentine's one which closes tomorrow. $100 prize.