Having a good laugh cause people being dorks in g-chat.
Roleplaying with peoples who don't suck at it.
laughing at stupid people on main
It's very good to start from scratch with nothing but your 500z and Novice gear... and make all your way up... it just gives me a nice feel!
My young archer(lv.40+) being chased by a ungoliath and it's porcelios, slowly killing it and gain a few continuous levels, AND get a pair of Boots[1], all in 1 go without dying. Of course, it's not on heRO. 
transing my HP with Vara, one of my first parties at the ice dungeon with my wiz, meeting sertain people, walking party with Aes, stupid guildchat conversations <3, getting married ingame and the after party x'D, PvP tournament where i won WOO!
etc. etc. etc
Getting on the /alchemist ranking. I wish i had an MVP card, at least I got a mobster card while taming pets.
One of the most hilarious moments I'd ever had was raiding the castle of an old guild of mine on another server. I hadn't played for a year; I spent all the money I had on an emperium, and snuck in during a brief moment their precast wasn't a wall of death.
Finnally Transing my Knight after months and months and months of lvling him
Oh yah I forgot one of my fave RO things which is also being challenged fighting hard in a dungeon.
When i found an Abysmal Knight Card on my 8th kill :3