Cash is a rational birthday present but inappropriate
Here is a clip from Seinfeld that I use when teaching Behavioural Economics. It seems rational that Jerry gives Elaine $182 for her birthday but it really is inappropriate. Cash replaces social norms by market norms and ruins the feelings usually evoked by a typical non-cash birthday gift. The deadweight loss of giving is the loss of efficiency that occurs when the value of the gift to the recipient is less than the cost of the gift to the giver. In this case, economists argue that cash would be a more efficient gift.