I know many would be saying this is a wrong proverb shouldn't it be 'You reap what you sow'. Ok as usual I am giving you a different version for the old proverb.
The old proverb means if you do something bad to someone you get back the same either from that person or through some other person. My version 'you sow what you reap' is the other side of the story.
I hail from Thanjavur a small town in Tamil Nadu,
Coming back to the topic above, I am using the above analogy in here, what normally people do is they treat others in the way they were treated, in other words they sow what they reaped. But I am going to speak only about the negative side of this(though I am B '+' ve always); we humans (I stress on the word humans I am not speaking of divinely bodies or mahatmas here) have this tendency of REVENGE.
The revenge is of different types, few give it back immediately which is far less dangerous and at times turns out to be a kick in the air with no impact at all. There is another kind, who have some psychotic touch to it (someone like me :P)who take the insult deep in to the heart and wait for that opportune moment to give it back with salt and pepper and the final and worst type goes to the extreme of giving it back in installments. (for people who have seen Vadivelu comedy I guess you can relate this to, "தெளிய வச்சி தெளிய வச்சி அடிக்கிறது")
This type of revenge is something very normal giving back what you received. For instance if a person gives you least importance when you give him special privileges show him how it will be to be at the receiving end but don't over do it.
Be a mirror and reflect what they show to you. I am in the process of sowing what I reaped off late, will tell you how it went once I am done. Cheers.