Some of my favorite memory of Runescape :
1) Team up with my 2 buddies to kill one of our "enemy". That time we could mashed right mouse button to close door / gate, we waited the enemy to go into the cow farm, my 2 buddies went in to attack him, while i was outside of the gate to make sure the enemy couldn't open the gate to escape. It was funny but cruel too seeing him kept begging not to kill him. (you lost everything when u were killed, nothing left)
2) Magic and bow's level weren't calculated into the overall Level that time (or affected the overall level very minimally). I created a character just to level up magic level, and used the char to kill any player that were similar level as mine. Usually a few hits will kill the opponents. No wilderness that time, players can attack anyone anywhere except the small spawning area. (within +- 3 levels)
3) Used a middle level char to check where was my main enemy's leveling. Waited for him to engage in combat (usually with the highest level mob), and then login with my main char to "help" the mob to attack the enemy. Successfully killed him and felt good
Most NOT fun moment :
1) After stopping the game for a few years, i login the game and went to adventure in the wilderness (i already prepared if i saw any player, i would just run away asap).
Went in pretty deep area, saw a group of 5 players walking toward me, i knew something bad would happen, so i started running away. Thought i could escape, but didn't realize Jagex added some abilities like "binding" opponent (no such skill before i quit RS). I tried my best to run but at the end i got killed while it was just a few more steps to leave the wilderness area. Pretty bad luck!