So, you're an evil dragon and...

[SangoProduction]

You're an evil dragon of great legacy. And someone scrys on you, because they are a foolish mortal who thinks they are allowed to set eyes on even a magic depiction of your majesty. They are casting it from too far away to be convenient to fly to. Hell to give your time to hunting down such a mortal would honor them much more than they deserve.

So. What can you do through the scrying attempt itself, to exact your horrible punishment? (Any true chromatic dragon's ability is available for use.)

[Hackulator]

Use whatever divination spells are necessary to get enough information about them to cast Demand on them, then Demand them to come present themselves to you, then eat them without ever leaving your room. It's kind of like ordering pizza delivery.

[Metahuman1]

Gate in a Fiend who's smart enough to understand that crossing you is a HORRIBLE idea, but is more than a match for a mortal, and send it to go sort the mortal out. Maybe an Enriyes or if you must get a Demon, a Succubus to get the drop on them.

Make sure they have orders to bring the corpse back and drop it off at your lair so you can mount it too the wall, pinned like a collectors butterfly, and do a ritual on it to show THAT image too the NEXT foolish mortal that tries this first, to give them a chance to turn back as it were with an, understanding, of what they are asking for if they try to Scry you, so you don't have to waste your time in the future.

[Selion]

You're an evil dragon of great legacy. And someone scrys on you, because they are a foolish mortal who thinks they are allowed to set eyes on even a magic depiction of your majesty. They are casting it from too far away to be convenient to fly to. Hell to give your time to hunting down such a mortal would honor them much more than they deserve.

So. What can you do through the scrying attempt itself, to exact your horrible punishment? (Any true chromatic dragon's ability is available for use.)

There is probably someone who worships your scaly beautyness and has failed you recently, this is a wonderful excuse for the poor fellow to regain your favor. You just have to summon your servant and complain that mere humans dare to feel safe from your anger just because they are so far away and such a nuisance doesn't deserve your direct attention, your worshipper, eyes filled with gratitude, would set sail immediately to prove her devotion

[rferries]

Keep detect scrying active on your person.

[Bronk]

The dragon could use the spell "False Vision" to deceive the scryer, perhaps to lure them in for an eatening.

It could also procure a 'Deathglance Locket' - or maybe a few of them - from the Dragon Compendium, which allows a retaliatory damaging strike through the scrying sensor.

[Telonius]

Remember: some things cannot be unseen. Use some twisted creativity.

Alternately, write this down (Arcane Mark will do, talon scratch on rock if not) and show it to the sensor.
"I eat one town for each time you scry on me."

[Segev]

Easiest answer: Make your save and cause him to waste his spell slot. Or have your SR handle it.

Failing those, keeping mind blank or nondetection up would be another barrier to it working at all.

False vision, as somebody else mentioned, means they always see what you want them to see when they scry on you "successfully." A good deterrant for general purposes is just you, in an otherwise empty version of your chamber, turning to look RIGHT AT the scrying sensor, and apparently through it at the caster. Just...staring.

If you know who it is and want to really annoy them, the false vision could be of you coming for them. In flight, on your way, possibly burning their hometown in passing. Even if they discover the lie by investigation, the fear, panic, and obvious threat will be sent.

There's also dream. They scried on you; visit them in their dreams. Or use nightmare to make the dream particularly horrific.

[Lapak]

Use whatever divination spells are necessary to get enough information about them to cast Demand on them, then Demand them to come present themselves to you, then eat them without ever leaving your room. It's kind of like ordering pizza delivery.
No need for a spell. You're a monster with over 21 HD and Diplomacy as a class skill; use an Epic Diplomacy check to turn them into a fanatic follower.

[Hackulator]

No need for a spell. You're a monster with over 21 HD and Diplomacy as a class skill; use an Epic Diplomacy check to turn them into a fanatic follower.

Diplomacy doesn't work on PCs, I am assuming this is an NPC dragon being scryed on by PCs.

[Deophaun]

You're an evil dragon of great legacy. And someone scrys on you...
...they are a threat. A small threat, perhaps, but they have succeeded in getting past my initial defenses. That warrants the entire kingdom in which they reside being turned to ash.

How do you think I gained my great legacy in the first place?

As for convenience, that's why Tiamat created greater teleport.

[NontheistCleric]

Why bother doing anything? This mortal is too far beneath you to merit even a moment of your time.

As for the horrible punishment? The mortal already lives a short, squalid life full of suffering. The punishment is for them to comprehend just how inadequate they are compared to your inestimable majesty.

[Crake]

Detect scrying and my far superior caster level will easily give me a vision or their current location and an image of them. Use vision to see if they're even worthy of being considered legendary, if not, teleport over to them and power word kill them, since they probably won't have the HP to survive it, if he is considered legendary though, then things become a bit more complicated, and devlove into typical high level wizardry shenannigans.