Collin Gosselin Fires Back After Mom Kate Implies He's Struggling with Mental Illness

Collin Gosselin says he's passed multiple psych evaluations with flying colors ... and his mom's the one who needs to get checked out.

We got Kate Gosselin's son in NYC hours after his mom implied he was struggling with mental illness ... and he returned fire.

Collin tells us he's grateful for his dad, Jon Gosselin, who he says has his back following the abuse allegations he leveled at his mom.

And as for Kate ... Collin thinks his mom is due for a psych exam.

As we previously reported, Collin's allegations are pretty disturbing -- he claims his mom once zip-tied his hands and feet together, and would pull his ear so hard that it would swell.

Max Naumov was also there with Collin, and they gave us some insights into being in the Malaysian jungle during season 5 of "Special Forces: World Toughest Test."

Kate shrugged off the claims on social media while responding to users who were sticking up for her ... and now Collin's clapping back.