Today's word is:
我がまま わがまま wagamama
(It's sometimes written 我が侭, but it's most commonly written as all hiragana or 我がまま）
It means to be selfish, demanding, care only about yourself, and so on. It is a word that can have a negative or positive connotation, but mostly it's negative. A wagamama child (我がままな子供）is synonymous with a spoiled/bad child.
It it most often used as an adjective, e.g.
あの人は我がままですね。 あのひとはわがままですね。 ano hito wa wagamama desu ne.
- That person is selfish, isn't she.
Sometimes it's used as a noun:
おもちゃ買ってなんて、我がまま言わないで！ おもちゃかってなんて、わがままいわないで！ omocha katte nante, wagamama iwanaide!
Don't say selfish (things) like 'buy me a toy'!
So what about that restaurant then?
According to the Wagamama Wikipedia page, the London based chain of 'TGIFA'* pan-Asian eateries "defines wagamama as "wilful / naughty child". I guess they mean that in a positive way.
If you want to see what I and others think of Wagamama, take a look at this forum topic over on Just Bento.
(*Thank God It's Fake Asian ^_^;)