And I say, “Thanks dude! Bavarian cream is my favorite!”.

Okay, nothing wrong with this, unless you knew the person wasn’t a “dude”.

And the office temp shouts, “I’m not a dude!” and pushes the coffee and donuts onto the floor. Big mess.

Obviously wrong, but a “I call everyone dudes, no offence meant” from you would show everyone in the room that you didn’t mean to offend them.

And I reply, “Nobody cares about your stupid gender.”

And now you’re an asshole. And a dumb one at that as not only you expressed your opinion about someone else’s “stupid gender”, but also turned others against you.

Assuming this even happened and you’re not leaving anything out, you need more “people skills”.