K: "K" is for curt and the texting equivalent of the middle finger. They have nothing left to say.
Yes.: Meaning, they are not happy about what they just agreed to.
Sure.: The period at the end sounds annoyed or dismissive, like the person you're texting has an attitude.
Yep: Implies an upbeat worry-free attitude, a la "yeah, totally, no problem!"
Yup: This is the pissed-off cousin of "yep" and indicates you've agreed to do something you don't want to do.
That's different: They're not a fan, but they don't want to disappoint or offend you.
That's fine: Obviously, it's not.
Umm yeah: Sarcastic response to a stupid question.
