Obstreperous means boisterous, noisy, aggressive, defiant. You’ve probably seen an obstreperous child in the grocery store, pulling away from her mother, screaming at the top of her lungs.
If you’ve been to a large concert where the band doesn't come on stage for hours, you might have been part of an obstreperous crowd: increasingly impatient, with fights breaking out, things thrown up onto the stage, and demands being shouted, "Give us some music before the night is out!" Some people are kind and gentle with strangers, but around their own family turn obstreperous, shouting "You never loved me!" at their mom when she gives them the smaller of two cookies.