Mhh, I assume they're roughly the same as RS3's :
- Muggers : North of Edgeville, nearby Aubury's rune shop and the mine west of Varrock
- Highwaymen : on the path near Falador's farm and the Crafting Guild
- Scorpions : Dwarven mine and Al Kharid mine
- Of course some mid-to-high level monsters are aggressive : hill/moss giants, SoS monsters and lesser demons.
These are all of the nuisances I can think of right now.
Edit : The Black Knights in the Black Knights' Fortress are also aggressive; beware of them when you're doing the related quest. Bring food with you!