Billface

The involuntary facial reaction produced by payer of bill upon observation of bill at time of payment at a restaurant or bar. This is discernible due to sudden albeit momentary change of facial reaction that is often masked by bill payer's efforts to divert attention by loud speech, reference to other events, reassurance that bill amount is far less than expected,etc. This reaction may be excessive due to unexpected amount or ever so slight even if the said amount was presumed. This reaction is only involuntary and genuine on the face of actual payer at the time of bill payment and will occur with certainty upon bill payer's face 97% of the time regardless of financial status.