As other answers have pointed out, it refers to a situation in which it's pointless to try because it's impossible to win: either you're going to get a hiding, that is, take a (metaphorical) beating on your hide, or else...nothing. There is nothing else. You're going to lose, and you're probably going to lose so badly that your opponent is going to gain nothing from beating you.
It's usually meant literally, but "tea" doesn't just refer to the drink, but refers to the meal known as tea. There are quote a few different types of meal called tea, depending on which country or which part of the UK you come from.
For example, there's "low tea", or "afternoon tea", usually a light snack such as sandwiches or eaten between 2pm and 5pm. Nowadays, this can also be a treat in a cafe or hotel with cakes, pastries, or scones and jam and cream. (See this book and this book.)
There's also "high tea", an early evening meal, eaten between 5pm and 7pm. This would be followed by a larger meal later on. Low and high refer to the height of the table where tea was eaten.
Tea can also refer to the main evening meal in the north of England, Scotland, Wales and Northern Ireland.
"Taking tea" is a common phrase for having this meal or snack or just sitting down to brew up, pour and drink tea; it is somewhat of a ceremony. For what it's worth, here's an Ngrams chart (and there's not much difference in shape between UK and US English):
"Children to compete for chance to
take tea with the Mad Hatter."
This clearly refers to the Lewis Carroll's Alice's Adventures in Wonderland where in chapter 7 the Mad Hatter is having a tea party. It's always six o'clock, and they're always drinking tea. There's bread and butter laid out as well:
'Take some more tea,' the March Hare
said to Alice, very earnestly.
'I've had nothing yet,' Alice replied
in an offended tone, 'so I can't take
more.'
'You mean you can't take less,' said
the Hatter: 'it's very easy to take
more than nothing.'
'Nobody asked your opinion,' said Alice.
'Who's making personal remarks now?' the Hatter asked
triumphantly.
Alice did not quite know what to say
to this: so she helped herself to some
tea and bread-and-butter, and then
turned to the Dormouse, and repeated
her question. 'Why did they live at
the bottom of a well?'
But as to the original question, the winning children would join the Hatter's tea party. There might be actual drinks and snacks for the children, or it could be meant that the winners would get to spend time with the Hatter.
Best Answer
To be nothing like means it is completely different and has nothing in common. Nothing like anything means incomparable; completely different from all other things. This is the literal meaning of the term, no figurative or idiom involved.
There are three examples of nothing like anything in the Corpus of Contemporary American English (COCA):
Here the speaker means the event was completely unlike any event previously experienced in the country.
Here the speaker is referring to some type of adversity that this time has a magnitude never before seen, incomparable to any previous adversity.
Here, whatever it is the speaker is experiencing is unlike any experience she has had in the same environment.