it basically means "stop lying", "I don't care" and "fuck off/fuck you" depending on the phrase it's used at.
first time used by two students (Z.Yacine and Y.Abdelfettah - around 2020) when they were looking for a way to insult their professor without him being aware of it, later on it became their way of insulting everyone, then the word caught others' attention and a variety of other students started using it.
origin of the word is ترخف
person 1 : believe me bro, I tried did my best but did not work person 2 : chisme.
or
professor : you have to solve all these eauqtions by tomorrow, if not you get an F.
student ; Sir, chisme.
noun. gossip noun talk about other people's affairs, not always truthful. stuff noun (unimportant) matter, things, objects etc. (Translation of chismes from the PASSWORD Spanish–English
And dying in yo' bed many years from now, would ya be willing ta trade all da days from dis here day ta dat fo' one chance, just one chance, ta come back here as young men an' tell our enemies dat dey may take our lives but dey will never take our freedom ... YUB NUB!