What does "tell me about it" mean?

Strong empathetic agreement with a complaint or difficult situation, NOT a request for more information. This is one of the most counterintuitive expressions in English.

"The commute is exhausting." "Tell me about it." = "I know exactly what you mean, I feel the same."

The phrase is a way of saying that you have lived through the very same thing, so you do not need any explanation. You are agreeing hard and fast, almost before the other person has finished speaking.

Literally, "tell me about it" sounds like "please explain further." But as an idiom, it means "I already know, there's nothing new to tell me, I've experienced this myself." The sarcasm is soft but present. The whole point is that they should NOT tell you about it, because you know all about it already.

Empathetic, solidarity-building. It says: we're in the same situation and I feel your pain. It is warm rather than cold, and it usually comes with a sigh, a laugh, or a knowing nod.

"This heat is unbearable today." "Tell me about it, I couldn't sleep at all last night."

"Kids are so expensive these days." "Tell me about it. Mine want new shoes every month."

"Traffic on the motorway was a nightmare." "Ugh, tell me about it."

Notice that a speaker often follows the phrase with their own version of the same complaint. That is the natural rhythm: first agree, then match the story with your own.

In casual conversation among friends this phrase is everywhere and feels completely relaxed. At work it is fine with close colleagues, for example about a long meeting or a tricky client. In a very formal setting, or with a senior manager you do not know well, choose something softer like "I completely understand" or "Yes, it has been challenging." "Tell me about it" carries a hint of shared grumbling, and grumbling is not always welcome in front of the boss.

The meaning is identical on both sides of the Atlantic. Americans may stretch it to "Tell me about it!" with heavy emphasis, while British speakers often deliver it drier and quieter, sometimes with a raised eyebrow. Either way it is understood everywhere English is spoken.

The classic error is answering the idiom by actually explaining. Imagine a native speaker says "Tell me about it" and the learner responds with a detailed account of their day. This is understandable but slightly confusing, because the native speaker was not asking a question at all. Remember, if someone says it to you, the correct reply is to keep sharing the complaint together, not to launch into a fresh explanation.

Picture two tired friends slumped on a sofa. One complains, the other says "Tell me about it" while rolling their eyes. Nobody actually explains anything, because they both already know. Link the phrase in your mind to that eye-roll of shared suffering, and you will never mistake it for a genuine question again.

A language learner responding to "tell me about it" by actually explaining further would be understandable but slightly confusing to a native speaker.

"I know, right?" or "Same here" cover similar ground but with less punch. Other close cousins include "You're telling me" and "Don't get me started," which pushes even further into shared frustration. "You're telling me" is especially useful, since it works almost exactly like "tell me about it" and also means the opposite of what the words seem to say.

"Preaching to the choir" is another agreement idiom. It means you are telling something to someone who already agrees completely, so there is no need to convince them. It sits nicely alongside "tell me about it" as a way to signal shared feeling.