Montana Tucker’s dropping a new single that’s all about self-confidence, but make no mistake … she has vivid memories of bullies tearing down her confidence and forcing her into bathroom stalls.

The singer dug into her pain locker to reveal what fueled “Be Myself” … her new single featuring Todrick Hall. The track aims to inspire self-acceptance and inclusivity … something Montana says she works hard to convey on social media, and in real life.

On Thursday’s “TMZ Live” she told us high school bullies called her MAN-tana because she was “a little bit bigger than the rest of the girls.”

The bullying got so out of hand, Montana tells us she was relegated to sitting in the bathroom for lunch every day.

Her official “Be Myself” music vid — which includes a flash mob routine in Times Square — drops Friday, and Montana says it will also draw on some of those experiences she and Todrick had in school.

As for cyberbullying these days … Montana told us how she deals with hate now, and she has an interesting take on people who hide behind keyboards to talk smack.