NPC - Romeo was a spastic. I wanted to bitch-slap him for being such an idiot, then go have sex with Juliet and finally solo KBD a few times. King Roald's advisor during the first or second Myreque quest - he's like a modern-day religious fanatic, lets Saradomin make all his decisions for him. Also used to think the Wise Old Man was a dick, built some respect back for him in Swan Song.
Monster - All scorpions. I've had a history with them dating back to 2003 - when my team of friends tried to enter the wild to go PKing, we got attacked by scorpions. Now when you have RS classic's 3-hit combat system, they're fucking lethal. The scorpion problem continues to this day. I'll be north of Edge doing some F2P no-arms, will get some epic combos, my opponent will stop attacking to eat and a scorpion will come and PJ me because for some stupid reason MvP takes priority over PvP.
Quest/Place - Mourning's Ends part 2, specifically the Temple of Light. What the fuck, seriously.