If you want to skill weapons skills for Master of Arms or Did Somebody Order a Knuckle Sandwich? Achievement, there is a very secure and easy way to do this while AFK, as gaining the last few skill points can take some time! My record was 30 minutes for 399 to 400!
The trick is very easy. Use a Dalaran portal to Shattrath and go to Shadow Labyrinth. If you’re level is high enough (lv 78 or higher, when the mobs turn in grey), simply go to the first boss Ambassador Hellmaw. He is banished (DON’T KILL THE MOBS IN THIS ROOM, or the will be set free!!!).
Go behind him and turn auto-attack on and go AFK. Because he’s banished he won’t ever die and when the trash mobs are gray to you, they won’t attack you either. Make sure to check out every 30 minutes or so to make sure you hit the cap of 400 and change the weapons for the next skilling.
Update 1: Seems it works with Gordok Spirit in Dire Maul too.