Dony, anyone you experience out there doing this is adjusting their personal MMR. The only reason they are adjusting their MMR is because they are encountering computer enemies (non-antag) destroying them in two bullets and they are frustrated. That is all it is.
Keep in mind, every match is a roll of the dice and you should play this game knowing that some matches will seem heavily favored in your regard, and then next match will be heavily favored in the antag's regard.
That is the nature of this game, and it's part of what makes it unique/addictive.
In the most recent livestream, they addressed this issue to say that MMR is changing to more naturally fit your personal skills and "how well you've done in the game" and that's a good thing, they know this is a an issue and are addressing it.
I speak from experience, I did a few days of jumping off the cliff to lower my MMR and as they said in the livestream, it was very unsatisfying to do that, game after game, to just lower the number. At a certain point - you will have to accept that on a match-by-match basis, anything can happen, just keep playing and grinding and it will all even out in the end.
MAIN POINT - NOTHING TO WORRY ABOUT
Just get your favorite character set up they way you like, get them up to the level where your weapon is a beast, and enjoy this game. If it's not for your, so be it, but know that this is a challenging game and that anything can happen. It's really as simple as that.
