You're often late yourself and you criticize me? That's the pot calling the kettle black.
Tips
memory
Tortoises and soft-shelled turtles BOTH have very stubby tails - so the tortoise mocking the 鳖 for being tailless is laughable hypocrisy. Picture two near-identical reptiles, one squinting at the other's barely-there tail.
usage
Common variants: 龟笑鳖无尾 and 乌龟笑鳖无尾. The English equivalent 'pot calling the kettle black' (五十步笑百步 is another close match) captures the meaning, but 龟笑鳖无尾 is more vivid and slightly more colloquial.
