Sabrina Carpenter References 'Saltburn' Bathtub Scene in Coachella Outro

Sabrina Carpenter incorporated Barry Keoghan into her latest outro ... referencing a scene from his flick "Saltburn" -- and leaving fans with a really raunchy line.

The singer-songwriter took the Coachella stage Friday and finished it off with her hit song "Nonsense." If you don't know, the track ends with Sabrina saying a couple lines -- usually sexual -- and she changes it up from performance to performance.

Friday night's lines ... "Made his knees so weak / he had to spread mine. He’s drinking my bathwater like it’s red wine / Coachella, see you back here when I headline!”

It's a pretty clever line ... and, if you check out the clip, fans go crazy for her bathwater lyrics -- 'cause it's a clear reference to her man Barry Keoghan's "Saltburn" movie.

Also, peep the shirt Sabrina's wearing with the Jesus reference on it ... another person known for turning water to wine -- just sayin'.

If you haven't seen "Saltburn" ... Barry's character laps up dirty bathwater left behind after Jacob Elordi's character washes himself -- oh and there's semen in the water as well, just BTW.

Sabrina's taken the sexual nature of the scene and twisted it here ... and, ya gotta think BK absolutely loved it. After all, he's one of SC's biggest fans!

Remember ... Sabrina gave Barry a little wave at her performance during Coachella's first weekend -- and, he seemed totally jazzed about getting the shout-out mid-performance.

They're also out in public together a bunch these days ... earlier this week, TMZ obtained exclusive photos of the dynamic duo just hanging out in Disney's California Adventure -- so, it seems it's getting super serious.