i think there is confusion everywhere in the world about that one... it can also mean get out of the way on a 2 way highway if someone is hogging the fast lane... for me, i very often use it at a u-turn if i think someone is going to cut me off and i think they wont hear my horn... at a round about i use it, with my window down and a hand signal, to indicate to the fools that they have right of way
another dangerous one for a car driver, that can be dangerous to a car but specially a motorcycle is the 'dead zone' in the door mirror where a driver cannot see on his right, if driving on the right, unless he turns his head before making a maneuver. most thais rely solely on their mirrors and cant be bothere to turn and look... prolly the cause of a GREAT deal of accidents here