Being a "jerk" is NOT dependent on weight! They come in all shapes & sizes! Most folks that I know that are a "little over their ideal weight" are a "jolly ole' bunch"...as a matter of fact, I know a lot of "skinny jerks"...
I certainly believe that a person is a product of one's environment (i.e. growing up, maybe they are a jerk themselves and can't make friends, perhaps a bit of genetic makeup, maybe they live on top of a toxic waste dump, chemical imbalance, maybe they maxed out their credit cards or can't get credit, maybe they just don't like you, maybe it's a certain color or barometric pressure that sets them off, one's ability to handle "stress", oh the list could go on and on and on...)...
Cheer up and try not to "stereotype" folks...maybe you have too many "jerk" acquaintances?
Seriously, no offense intended here...there's just a lot of reasons for folks to be "jerks" - I try and ignore them. If you let them get to you, then they are winning "the game of life"! There's a fellow at work that will let "his chain get pulled" a little too easily. Folks tend to "pick" on him...that's not right. I'm the opposite, I try and teach him how to handle the "jerks"...mutual respect is the name of the game. Kill em' with kindness, it makes em' even madder and then you can go off smiling!