unrelated consideration?/ Help please..?

is there such a thing as unrelated consideration which would help in breach of contract case?
Please state the laws or terminology I can review that cover this type of scenario as I cant properly put this into words.

For example; a man accuses a video rental company of not fulfilling an oral contract to provide him with a brand new boat if he purchased the new Bingo James DVD…
Can the video rental company say the man held unreasonable expectations given the business conducted by the video rental company is totally unrelated to what the man is asking for??
What is this called? Even a push in the right direction will help
(Yes I know an oral contract isnt worth the paper it’s written on but let’s look beyond that for this examples sake.) Thanks