The rapper was performing at the European Lollapalooza in Stockholm Saturday, and right in the middle of one of his songs -- a loose item sailed in the air and landed at his feet. Nas X stopped the show and bent down to see what it was ... as it turns, it was a sex toy.

Then came his obvious question ... "Who threw they p**** onstage?" The reason he's asking that is because is something that's meant to mimic a vagina -- yep, we're going there!

Anyway ... it was no harm, no foul in the end. Nas X wasn't hit, and it doesn't seem like the interruption sidelined the show at all ... like we said, it amounted to more comedy than anything else -- but this is still very much part of a larger trend that's becoming concerning.

Bebe Rexha's phone-to-face incident certainly stands out as one of the more gruesome acts of stage chucking that have gone down recently -- but she's far from the only one who's had to deal with intrusive fans in the crowd. It's a thing lately ... and it's not great long-term.