did i say they were my friends?

In the case of naughty players, I've seen in my experience that the best thing the DM can do is to show them in-game that being an ass is not going to bode well for them. Naturally, there are going to be NPC's that are critical to a story arc or things that the DM has set in stone, but the players will try to **** with anyway. You can always punish them for being idiots:

>your party arrives at the monastery the next morning, you are tasked with meeting an ancient elf and gathering what knowledge he has of the Reckoning
>the first monk to approach you says, "Ah, visitors! Come, come, Master Kujo is waiting to speak with you"
>party follows
>you arrive in a tent where a blindfolded elf sits cross-legged before a strange stone with a rainbow of different colored runes etched on it
>he waves his hand in signal for the greeting monk to leave the tent and begins to speak, "I have foreseen a dark future, one that-"
>I GO TO SWING MY AXE AT HIM
>okay roll for it
>rolls anything but 20
>alright as you go to swing, he catches your hand, looks you dead in the eyes (despite his eyes being covered), twists your wrist and bows you into submission
>okay who next?
>NO I'M GONNA PUNCH HIM WITH MY LEFT HAND NOW
>...fine roll your goddamn dice
>rolls anything but 20
>as you go to punch him he kicks your fist, breaking most of your fingers

At this point one of two things will likely happen. Either your party will understand that not every NPC needs to be fought, or they'll all try to jump him. If they all try to fight him, your party is pretty much a lost cause. Throw them into a campaign centered around an arena pit, throw a Monster Manuel at them, and let them DM their own campaign with no story.