Rock and a hard place. 

Deciding on a negative permanent situation or another negative permanent situation.

It's my wife or my girlfriend. Im stuck between a rock and a hard place.

She's stuck between a rock and a hard place. She is taking a hard dick in the ass and a rock in the pussy. Or visa versa. A sexual fantasy position. Also known as Double penetration.
Some dicks are referred to as hard as a rock, some dicks are hard.

Rock and a hard place. by Fireann Steele November 29, 2019

rock and a hard place 

in a tight spot; having to make an impossible decision; a lose-lose situation

Shack wants to go to her best fish's birthday, but she already promised to go out of town with her friend. she is between a rock and a hard place.

rock and a hard place by don't hate me February 4, 2005

Rock and a hard place 

Having to choose between two undesirable situations

Some of David Letterman's female employees were caught between a rock and a hard place; They either had to sleep with a cranky and humorless old man or risk getting passed over for promotions by women that were.

Rock and a hard place by Mr Wilhelm October 8, 2009

between a rock and a hard place 

describing a situation where you have to make a decision that you don't want to make.

you got me in between a rock and a hard place; alright, i'll let you borrow two grand.

between a rock and a hard place by 5150 December 4, 2004

stuck between a rock and a hard place 

You're damned if you do and you're damned if you don't

Either way you are in a mess and big trouble. You just aren't doing to well.

When my wife walked out because I wouldn't help her becuase I thought what she was doing was wrong. She gave me the choice to change my mind and follow her, if I really loved her, or sit at home and never see her again. I was really stuck between a rock and a hard place.

stuck between a rock and a hard place by NikkiMac August 9, 2007