A roll in the hay
Definition 1 of 1
Pro Tip 1/3Casual Connotation
This phrase implies a carefree attitude towards sex, without emotional attachment or serious commitment. 
They weren't dating; it was just a roll in the hay.
Pro Tip 2/3Idiomatic Expression
'A roll in the hay' is an idiomatic expression and shouldn't be taken literally; it's a metaphor for casual sex. 
After a few dates, they were ready for a roll in the hay.
Pro Tip 3/3Slang Warning
Be cautious using this phrase in formal situations; it is slang and could be considered inappropriate or unprofessional. 
In a business meeting, he jokingly suggested a roll in the hay, which was inappropriate.