Odds and sods — another English version of bits and pieces
Have rocks in one’s head — be stupid. (Slang; 1940s)
Cool as a cucumber — calm, relaxed, in control of your emotions. (1732)
Lie low — keep out of sight, bide one’s time (Shakespeare, 1599)
Alike as two peas in a pod — two identical items or people (1500s)
Going like sixty — very fast or with great force
Useless as tits on a bull — utterly useless; bull tits don’t give milk
Slackass — a hybrid of slacker and jackass
Knee-high to a grasshopper — very small or very young, US, 1814
Thick in the head — slow to catch on
Sound like a broken record — repeat the same words with little variation
This last expression derives directly from the term involving polyvinyl record albums, where such a “broken” record would repeatedly skip back a moment in what being played. (The term was inaccurate – usually such skipping was caused by debris on the disc.) First recorded in 1940 and was popular enough to be the title for several songs.