日語 Japanese Ask Questions Thread2 質問

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Japanese - Ask questions thread
http://dis.4chan.org/read/lang/1174719097/l50

There's a lot of requests and demands in Japanese and I'm curious where this one belongs as you won't ever learn it in class. It sounds like bad grammar but it isn't.

It's like this
待つんだ！
or
ここは俺に任せて先に行くんだ

Is it a request? Is it a demand? Is it even used in real Japanese (outside of TV)
Is it rude?