Overwhelm, bedazzle, or amaze someone, as in The young pianist knocked the socks off of the judges, or That display will knock their socks off. [Slang; mid-1800s]

Also, knock the spots off. Surpass or outdo completely, defeat. For example, These large chains have been knocking the socks off the small independent grocers, or Our team knocked the spots off them. The spots most likely allude to target practice with playing cards where the object is to shoot through all the pips, spots, or marks indicating the suit or numerical value of a playing card, but one authority holds that they were used in a horse-breeding context and meant “to be in the vanguard.” [Mid-1800s]