To come back on OP, it was with a girlfriend. She was living with her parents and had a bunk bed with the bed at the top.
Somehow her dad has an office in a kind of recess corridor behind her room.
We were just chilling on the bed and then suddenly she puts her hand on my belt, take it off, unbutton everything and goes down.
Plot twist: her dad was in his room (basically there is like just a wall separating us on the bed and him behind).
I am not very vocal but I began to be a little bit and she stopped before the end unfortunately because we didn't want her father to burst in suddenly...
Although short lived, the adrenaline and spontaneousness made it very memorable.