grasp at straws

To make a desperate attempt to salvage a bad situation. A: "But what about all those times I took the trash out when you hadn't even asked me to?" B: "That has nothing to do with why you're in trouble now, so stop grasping at straws."

Fig. to depend on something that is useless; to make a futile attempt at something. John couldn't answer the teacher's question. He was just grasping at straws. There I was, grasping at straws, with no one to help me.

Also, clutch at straws. Make a desperate attempt at saving oneself. For example, He had lost the argument, but he kept grasping at straws, naming numerous previous cases that had little to do with this one . This metaphoric expression alludes to a drowning person trying to save himself by grabbing at flimsy reeds. First recorded in 1534, the term was used figuratively by the late 1600s.

To make a hopeless effort to save oneself. The term comes from the ancient image of a drowning man clutching at insubstantial reeds in an attempt to save himself, and it often was put as to catch or clutch at straws. It appeared in print as early as the sixteenth century and soon was regarded as a proverb. Indeed, Samuel Richardson so identifies it in Clarissa (1748): “A drowning man will catch at a straw, the proverb well says.” An earlier usage is “We do not as men redie to be drowned, catch at euery straw” (John Prime, Fruitful and Brief Discourse, 1583).