[deckiedan]

It's older than just "a slogan about sexual assault".

"No means No!" is a common parenting phrase to teach kids when a parent says "no", they mean it. If you asked for an ice-cream, and I said no, then stop asking again!

I have no data on the origins on the phrase in English as such, but certainly the concept has been around even back to the 1st Century - with the Phrase "let your yes mean yes, and your no mean no, everything else comes from the evil one" back in Matthew's gospel (5:37).

[skybrian]

You have to go by what it means today. The meaning of phrases (especially implied meanings) changes based on what happens. At one time, "gay" just meant happy, and 9/11 was just another date.

[whamlastxmas]

I think it's fair to say it's in a transitional phase at worst and while it would be ideal to avoid one cannot assume the connotation in every single use.

[deusofnull]

"No means no" is also currently a common parenting phrase to teach kids about what to say if someone is touching them in inappropriate ways.