Do me a lemon, you really think I believe that story?
do me a lemon
idiomExpresses disbelief.
Origin
disputed origin"Do me a favour" (rhyming with "lemon flavour") in Cockney rhyming slang.
When he claimed he won the lottery twice in one week, I told him to do me a lemon.
She looked at me with utter skepticism and told me to do me a lemon after I suggested the project would be finished by morning.