Mercy is in such short supply upon the Earth today that the small measure we do possess, we tend to hoard it up for ourselves when we should be giving it to others.
I wrote a poem once about someone who I thought didn't deserve mercy, it went like this:

I love to wind you like a spring.

Up, up up. I can twist, twist, twist,
till you break into shouting
Or you burst into tears.
I don’t care.
I do it because I can.

I do it to you, because it’s funny to watch you fret.
But I just don’t care.
I mean, I really get a kick from kicking you.
And making you mad
And making you dance with rage,
As the springs inside your head snap and
Your legs buckle and bend as your teeth grind in time.
I know I should stop.
But gosh, you’re so damn funny when you get wound up over nothing.
Well, nothing that matters to me, anyway.
And Mercy seems so scare today.

The last line sums up the general attitude that pervades our society today.
Mercy is something you must first deserve. If you behave unmercifully then you shall be treated without mercy. Tit for tat, take that you dirty rat.

I know a lady and she is really, really MEAN! She frequently needs a mercy slap or a mercy clubbing but I don't think it will make her any nicer.
In her twisted mind she is getting what she deserves. Secretly she hates herself and believes that she is rubbish that must be kicked into the gutter. Her way of compensating is to hate others and treat people like rubbish. On days when she hates herself alot, those around her get especially large kickings that are meant to propel them into the nearest sewer.
Jesus said,"Blessed are the merciful for they shall receive mercy."
I think if we all waited till we deserved mercy we might have to wait along time especially if we expect nercy from our fellow man and woman.
The mean lady that I know doesn't deserve mercy but she badly, badly needs it. Someone needs to give her a break from herself and someone needs to love her and help her see that she is good and valuable, if only in the eyes of God, especially when she is being mean and horrible.
That's what mercy does, it loves and cares for the unlovely when no one else wants to.

Also in the book of James in Chapter 2, it is written that mercy triumphs over judgement.
It is so easy to judge but it takes faith and courage to extend the hand of mercy to an enemy who may bite it off and throw it in the gutter.