Here is my 100% Achievement Guide!
This happens not long after your first achievement.
When you enter the next room, you see a pinata and
Go into the next room to see a maintenance guy working on something, ignore him for now, doirectly infront of you is a long broom so pick that up.
Go back to the left and enter the room with the pinata again, click on the pinata and achievement will unlock.
Go to 2:40 to see how it is done.
Hope this helps!