Long about 1990 in Des Moines, I heard it confidently asserted that if you told someone to “shut up,” you were really saying “meet me in bed in five minutes.” One person said it was French.
I’m not sure anyone, anywhere, ever actually used “shut up” as a “Netflix and chill” -type euphemism for sex. Even in 1990, most of the kids I knew seemed to intuit that this was pure BS (or that, in any case, most of the time someone told another shut up, there was no hidden meaning), but it led to some giggling for a couple of weeks. By the time I was in middle school, I was in a group of other middle schoolers from other schools, and when someone (from a school on the other side of the metro area from me) said “Some people say ‘shut up’ means ‘meet me in bed in five minutes,'” there was a chorus of groans. “That is so old,” someone said. “And so immature,” said another.