Buckle up Buttercup is a sarcastic expression, denoting that one should get ready for some upcoming unpleasant or extreme action.
It is a bit of a sarcastic portmanteau between the "buckle up" phrase used to get people to use seat belts and "pucker up buttercup" meaning to prepare for a kiss. The sarcasm reverses the positive connotations.
My girl gave me the butterup when she heard I lost my job & she said they through away a genius of infinite perplexities.
My blind date gave me an eye opening butterup when he saw my figure & he said architects builds dreams. An artists reveals his innermost expressions, but as I lay stunned adjusting my structural integrities called eyes; I can say now and forever I know what it's like, to be in the presence of mastered magnificence.