Here's two creative insults that have stuck in my mind for many years:
He fell out of the dumb tree and hit every branch on the way down.
He can't pour water out of a boot that has instructions on the heel.
Winston Churchill was also known for his creative insults. I'll paraphrase one for you:
Lady So and So came up to Winston Churchill, wanting to insult him.
"If I were married to you, I'd poison your coffee."
To which Churchill blithely responded
"If I were married to you, I'd drink it."
More Churchill quotes:
"He has all the virtues I dislike and none of the vices I admire."
Correspondence between George Bernard Shaw and Churchill
Shaw to Churchhill: “I am enclosing two tickets to the first night of my new play; bring a friend... if you have one.”
Churchhill to Shaw: “Cannot possibly attend first night; will attend second, if there is one.”
Insults between Lady Astor & Churchill
"Sir, if I were married to you, I would serve you posion in your wine."
"Madam, if I were married to you, I would drink it."