Derived from the word "platonic," meaning "friendly," and also used as the opposite of romantic. "Play-tonic" is used to describe a "friends with benefits" situation. Their relationship is platonic, not romantic, but it also includes "play," or sensual/sexual interaction.
Person 1: Hey dude so are Mike and Jen just friends, or are they like a couple now?
Person 2: Neither, it's totally play-tonic.