Bottoming-out.
Known to happen to those of us with low-riding vehicles when we underestimate a speed
bump or curb and --*eeeeesh!*-- end up momentarily having the speed
bump or cub bump up kinda hard against the
tender underbelly of our vehicle.
This term has another, newer, meaning though and of course it's a sex
one.
"Bottoming-out" in bed is also when a woman is straddling her
male partner and, only when her partner has a long-
ish member, she tries to go deep and rest herself on top of his hips but *-eeeeesh!-* it's too long and the tender underbelly (her cervix or just the dead end of her birth canal, so-to-speak) is bumped kinda hard up against by the aforementioned member.
Women make the same exact face when either happens.
Bottoming-out.