Does working manual labor naturally make your personality rougher??

I think it's a fine profession as long as you are personally satisfied with it,
but strangely, whenever I see my friends who do manual labor,
every time we meet, they are complaining and grumbling about the world, spitting while talking about politics...
Seeing them change like this..
makes me want to avoid meeting them.
I seriously want to tell my friend to stop acting that way.