If you don't have anything nice to say don't say it at all

I'm a mocker. Those of you that know me know this is true. I'm honestly torn a lot of the time on if it is right or not.
One of my favorite past times of old is to just watch people and systematically mock them. Before I was saved I would routinely seek out the weaknesses in people and exploit them, I would intentionally wound people, just because I could..and mostly just because I was trying so desperately to hide my own hurt.
I mean, people are funny, they are down right odd most of the time, myself included. I can take it just as well as I can dish it out. But when is it to far? When does it cross the line from good old fashioned ribbing to mocking, in a cruel way? Does it make a difference if the person can hear you or not? Does it matter if you know them personally or not?
Frederick Buechner says:

We also know that words spoken in deep love or deep hate set things in motion within the human heart that can never be reversed.

When I read that the first time I of course understood the ramifications of speaking things hatefully, callously to those that we love, those that we directly communicate with. But surely it doesn't matter when I mock those that I don't talk to...when I do it in the shadows with other people that also don't know those that are being mocked.
In that case, I don't think the motion happens in the heart of the people I'm mocking, I think it happens in mine. When I mock people I don't know, I set things into motion in my heart that can never be reversed. When I speak things that are cruel, and mocking I change my heart a little. I blacken it and push God out of it a little. That grieves me.
When I lift people up with my speech, when I am the person that goes against the norm of conversation and give them the benefit of the doubt for their behavior, when I don't pick apart what they're wearing, how they're acting, what they're doing with their day, or life even, I set into motion righteous things in my heart. I'm just happier I think.

A few years back I went dress shopping with my mom for a wedding I would be reading in. It was VERY important that I look nice at this wedding because John would be there with his new fiance and I couldn't look like some schlub. I'm in the dressing room and mom is telling me to shuck off my pants so I can get the skirt on....I start to freak out on her because I don't want people to know what I'm doing in the dressing room. It was a dressing room, what were people going to think I was doing! For so long, and sometimes still, I get this almost paralyzing social anxiety because I think going out into public that people will mock me, ridicule me, and just all around find everything that is lacking about me. On one hand, this is such an egocentric feeling, because honestly most people couldn't care less about me. But on the other hand, I feel this way because I know it happens. I know it happens because I have been that person, I have been in that group of people and I have mocked and picked someone apart until there was nothing left to mock. That is the motion my mocking has put into place in my heart.

I don't know where the line is, I can't figure out when it's just good natured ribbing and when it's mocking. But I really want to.

Blessed is the man who does not walk in the counsel of the wicked or stand in the way of sinners or sit in the seat of mockers. But his delight is in the law of the Lord and on his law he meditates day and night.

Psalm 1:1-3