Iggy Azalea says she tried to warn Nick Young that his boys trip to Vegas last weekend would "look bad" in the wake of the whole cheating scandal ... but he went anyway -- and she's cool with it. 

The rapper says her fiance actually had a pretty good reason for the trip -- and it wasn't to party and go crazy ... it was more business than pleasure. 

We asked if the fact she went out sans engagement ring over the weekend was a message to the NBA star -- but she shot that down hard ... saying she doesn't think women have to rock the rock 24/7. 

"It's nothing personal ... it doesn't go with the outfit."

Long story short ... seems Nick's out of the doghouse and the engagement is still on.