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ABC News reports that a couple in the UK found an envelope stuffed in their 5 year old son's backpack when he came home from school recently. The envelope contained an invoice from his friend's mother for not showing up at her son's birthday party. The bill was for about $24.00.

The parents initially said their son would attend the celebration, but later realized that they already had plans that day with family members. They didn't bother telling the party host that the their son wasn't going to show up. The birthday boy's mom was livid.

The invoiced parents confronted the woman who sent them the bill and told her they aren't paying. She's threatening legal action.

Etiquette experts seem to think they're all being jerky. No, wait - that's me who thinks that. Your thoughts?