1.)In the MMORPG Furcadia a twink is someone who lacks character.They could simply use dialouge without action, or action without dialouge (Persona Playing).
They could be a auto-hitter that no matter what happens their attack inevitably hits you.
They could be a god-moder that can take anything and keep on coming, or have some unimaginable powers that where given to them by all their 'gods' of the universe.
Power-playing is in essence the same as god-moding where people fight and are able to do anything they wish without so much as trying.
Cont. breaking, people who leave a continuity due to fear of their characters death or serious harm, poofing out of a fight, or using a excuse to get out of the fight.
Post-and-Run RPing is where you come up, attack some person, then run away from the continuity.
Netspeaking (Optional) using anoying netspeak (IE: u,ur,iz,omg,rofl).
Twinking is a huge field and is hard to provide many examples to.