yeah it's very common to drop the ne in colloquial talk

I remember I was going to be late to a meeting with a French friend of mine. So I texted him telling him I would be a few minutes late. He texted back, "C'est pas grave." So while I still use the ne...pas constructs, I actively listen to French speakers to learn better how to speak French normally, and drop the ne when possible.

The others have provided some really good answers! I will just add on that I translate 'pas' (literally) into 'not'. It helps me make sentences without the ne.. .

I'd like to know too. I remember people in casual conversation doing this years ago, and it was not correct then, even if used often.

From my experience, I would juge that is handled comparibly to the contractions in English - you do not find can't, shouldn't, won't etc. in formal English speech either. In French the point of leaving the ne out is maybe a bit more colloquial, but not much.

It's a very common feature of spoken language. Listen to TV or radio or pop music and you'll hear it all the time (like this https://youtu.be/K3HeR6AuT5Y ). It seems almost universal to me and was used in the classroom when we were learning French at school.

Duolingo can't make up its mind about colloquial language - it rejects this but then actively teaches far less acceptable constructions in English that would actually make a fool of the learner.

I agree with the others, I've definitely heard it, I've even used it, but it's pretty colloquial. I wouldn't say "je sais pas" in a formal or exam situation. I've also heard it used poetically - with the disclaimer that I have no idea if it's more common in Canadian French, I'm sure Céline Dion even has a song that's called "Je Sais Pas"? Okay, forgive me if I've misremembered, but the phrase je sais pas has these lyrics in my brain: je sais les hivers, je sais le froid, mais la vie sans toi je sais pas.

For me it would fall into the category of know it exists, use it in informal situations, be wary of using it in formal/exam settings. I'll be honest and say I don't know if it's equally applicable for all verbs, but for savoir and être, I'd say it's fairly common.

Pas mal!