Translation plz! What does it mean when someone says 'Well thats an understatement...."?

Sort of - in the situation you described, the more correct thing to say would be: 'thanks for stating the obvious.'

Say if someone was OVERLY drunk - like, completely off their heads drunk and then they said something like, 'I'm tipsy' then it would be appropriate to say, 'Well that's an understatement.'

You would say that phrase when someone uses a watered down statement to what should really be said. An understatement is like the opposite of an exaggerated statement.

They mean that the person is being too conservative in their words.

For example, if someone said "The events of 9/11 were bad." That would be an understatement. The events of 9/11 were actually tragic, horrific, awful, nightmarish, etc. They were REALLY much WORSE Than 'bad' so the word 'bad' didn't come close to the actual definition of what happened. That's an understatement.

Yes, in one way it can mean that. I think it has become a generic phrase that people just say, not always applicable to the situation too. That's probably why you don't understand it. Like in your example, "You are drunk." "Well, that's an understatement!" It would mean 'you are really, really drunk.' Like being "fubar"-ed. That means fu**** up beyond all recognition. Stating that something fubared was merely drunk would be considered an understatement. Did that help you understand it better? Hope so! =)

It doesn't mean it's obvious. It means you have described something modestly, you've been nice, or held back. State- say, tell and under- below, beneath, less than.

You could also say "indeed". The meaning would be essentially the same. In- residing near the vicinity of.. and deed- debt= With debt. It means what you've said and more. Another common one is ", You can say that again."

it means that your remarks do not fully take into account the situations. The British are masters at understatements, like when the German's were bombing their cities the weathermen would report slight air disturbances in the air.