Subtlety is dead, put your cards all on the table (and then both climb on the table...)
A6 card and envelope, blank inside for your dirty message.
Sent via Royal Mail standard first class (non trackable)
Delivery to UK in 1 to 2 working days
Delivery to Europe in 3 to 5 working days
Delivery to the rest of the world in 5 to 7 working days