Toss the boss is a drinking game promoted by
publicans in
Australia.
For a limited time, (say, between 5pm and 6:30pm), the publican will put out the sign that offers the game. Punters (drinkers, in this context), will, when buying a "round" of drinks, call heads or tails of a coin flipped ("tossed") by the publican. If the punter wins, the round is on the house (the "boss").
Toss the boss is effectively Happy Hour, with somewhat improved revenues for the house, and all the fun of a boisterous drinking game.