Katy Perry and Justin Trudeau took their romance public Saturday night ... the lovebirds went out on a date in Paris, France, to celebrate Katy's 45th birthday.

Demi Lovato's ex Max Ehrich is getting super familiar with Florida law enforcement... because just weeks after being arrested for nitrous oxide possession, he was cited for driving the wrong…

Ray J says a knockout and four nights in the hospital still weren't enough to retire Reckless Ray ... 'cause he's got more crazy stuff to do before he finally…