when you have to say something nice to your boss or teammates or if you just finshed your task given by your team lead.. you nicely end the mail by saying thanks and regards but in reality you are cursing the hell outta thm.

Why worry? Used to tell someone not to worry.

Hakuna Matata.

someone who is always getting tensed, has high b.p, low tolerance for bullshit, someone who is easily annoyed

Think about it.

Piss off!

Literally, "So you want me to dance?" or "So you want me to jump with joy?"

A sarcastic retort designed to mean that one cares very little for what you've just uttered. So if you've just tried to impress or mollycoddle me, this rhetorical question is meant to insult you.

stop irritating me...

Literally, "You don't know who my father is?"

Employed as an intimidation tactic to imply power that makes you politically superior to the speaker, and therefore untouchable by the law.

Most frequently used when pulled over by a cop / frisked by airport security / otherwise faced with authorities against whom normal (non-father-famous) people have no viable defense.

N.B.: It is not always clear whether the father in question actually has important powers; quite often it's the approach (potential father-name-dropping) rather than the father's actual identity that's the intended killer weapon.

Used in written communication. To presumptiously thank someone in anticipation of a favourable response