They're looking for attention. ANY attention. Call them on this and people of this sort will often explode.
When they do, authority busts 'em down a bit.
ie: "I know you're just trying to get attention by bothering me."
If you want, you can add a taunt on the end, like "...due to your insecurity." or "...you must be awfully desperate." or mild somesuch. Be sure to deliver the line in a dead serious manner. I recommend
against taunting, though, as bullies are generally better at it, will get you emotionally involved, and then pissed off. When you get pissed off, they win. Just like the internet.
The best (and most egotistical!

) way to avoid becoming angry is simply thinking "He's not important enough for my attention." It's like having an /ignore list.
Make sure the bully understands that you don't care about his self-serving "rules" against "telling." Your masculinity and pride are not at stake. "Telling" means you are clever enough to use the system to your advantage, and courageous enough to admit when you can't fight. Authority figures don't like malcontents.
I've pretty much gotten over taunting back, as I can best most my age in logical debate, but not in base stuff.
"Dude, [insult]"
"Right. Good for you."
"You [insult]."
"Your opinion is of no relevance to me."
"[insult]"
"Of course." ("Sure." "Very mature of you." "Totally proves your point," etc.)
[Dude leaves.]
Edit: Pity works sometimes too.