A school-boy error. And the concealed throw, which in the spoof context might be, for instance, the 'wishing-well', which involves putting an elicit fourth coin into the spoofing hand and allowing it to 'accidentally' drop out of the hand. Cheap but cheerful. Spoof' isn't a drinking version of RPS, but a different game altogether albeit with some of the same psychological characteristics. Each player gets three coins.
All players then raise their clenched spoofing hands to signify that they've made their decisions.
Then, the players take it in turns to 'guess' how many coins they are collectively all holding e.g., if there are 3 players, the maximum collective total is 9 and the minimum is zero. Anyone who estimates correctly 'wins' and drops out. Successive rounds are played until there's only one person left who is the loser and must perform some forfeit, drinking penalty or whatever. The skilled initial caller can bluff rookie opponents who most likely are likely to be employing the standard linear-interpolation calling algorithm. A school-boy error.