Fuck you, that's why 

A response to a question of the practicality of something which is clearly overkill, it implies that the one who uses the phrase to answer the question of 'why' knows full well that it is overkill, and overkilling for overkill's sake was their intent.

(The examples probably describe it better)

Q: Why would you build an aircraft carrier that flies?
A: Because fuck you, that's why

Q: Why would you need a 6-core CPU?
A: Because fuck you, that's why

Q: Why would you make an automatic grenade launcher?
A: Because fuck you, that's why

Fuck you, that's why by gnerd October 11, 2011

because fuck you that's why 

When no explanation is necessary.

Douche: yo, why can't I get some of that azz?

Hot chick: because fuck you that's why.

because fuck you that's why by Supadupaflye69 August 12, 2014

Why? FUCK YOU, that's why. 

What someone says when they have done something for the purpose of maliciously disrupting another person(s) motive, intentions, life, job, etc, and the victim asks that someone why they did it.

NEWS AGENCY: We have hired a new science editor.

Bob: Welcome to the team, Freeman. We need you to start by editing this paper on climate change. Exxon is one of our top sponsors and they have told you to remove the bit on 80% efficiency solar panels and make it look like oil does not harm the environment.

Freeman: Ok.

3 days later:

Bob: FREEMAN! You included the bit on 80% efficiency solar panels, you made the bit on oil seem even more against the environment, and then you proved that Exxon bribes us! WHY?!

Freeman: Why? FUCK YOU, that's why.

Why? FUCK YOU, that's why. by The Lion's Word July 20, 2011

Fuck you that's why! 

The correct response to a smart arsed sarcastic question, usually from your partner.

Gemma :"You have apparently took a wrong turn and are now going in the wrong direction. Phils house is the other way, why did you do this?"
John : "Fuck you that's why!"

Fuck you that's why! by KingPryle September 25, 2010