That's the cop's sort of "catch-all" if they just really want to arrest you because they don't like what you've said, or how loudly you've said it (despite there being no laws against these things).

They can claim that you were causing a disturbance by shouting and making "obscene gestures". It's retarded that "obscene gesture" is a concept in the USA's legal system (1A should overrule that entirely), but that's how a cop will arrest you if you call him faggot a bunch of times after he gives you a ticket or something.

With bodycams, we have more insight into how cops operate than ever before. After incident is over, and the "suspect" is not resisting or is in custody, the cops always go off and have a pow-wow. I've seen several of these now, where all of the cops are like "Well, technically, he didn't break any laws. He's an asshole, though." Inevitably, one pipes up with "Well, I could hit him with a disorderly conduct/disturbing the peace, maybe obstruction."

And you're right, these charges are almost always thrown out before the defendant sees court. It's just a way for the cops to ruin that person's day, week, and who knows how much more. It's how they hit you without actually striking you.

Very likely, it's fairly easy to get out of that one by just "had a bad day, stress at work/home bla, bla..."