Another day, another fan who doesn’t know boundaries … this time, one shameless concertgoer took things way too far by reaching up to grab Halsey’s butt — mid-performance!

As you can see, Halsey was performing “Is There Somewhere” in Washington, D.C., earlier this week when the unidentified fan in the crowd reached dangerously close to her thigh … then brazenly slid a hand under her leather skirt, copping a quick feel in front of everyone.

The disturbing up-close clip — shot from right behind the creep — shows a gloved hand, presumably security, finally stepping in to swat away the paw … but TBH, it takes way too long to happen.

The clip’s blowing up online … with people once again yelling the obvious: keep your damn hands to yourself!!