When a cheap person regifts something and the reciever unwraps it to discover it is blatantly secondhand.
My friend regifted my DD an Easter egg sticky-taped to a dirty coffee mug, which had coffee residue and spoon marks in the base of the mug. Regift fail.
When someone re-gifts you a gift, and doesn't even realize that it is a gift that you originally gave them.
My friend totally regifted me a necklace for my birthday that I gave her for Christmas a week before!! Regift fail.