If you're looking for a mean-spirited birthday message, this one should do the trick!
Details:

Size: A6 (105 x 148mm / 4.1 x 5.8 inches). - that fits as a standard sized letter in the UK mail.
Printed on FSC Board - this means that the paper is produced from sustainable forests and/or recycled materials.
Blank inside for your own message.
100% recycled brown kraft envelope supplied.
Made in the UK.