You are more likely to lie after doing something good.

The moral licensing effect causes people to engage in unethical behavior after they have recently performed an act of moral virtue.

Participants who were asked to act as 'green' consumers were significantly more likely to cheat on a subsequent task to win a reward. By establishing a 'moral credit' through a prosocial action, individuals grant themselves subconscious permission to stray from their standards later. The positive action does not build character; it provides a license to be selfish.