It means "I'm not lying to you". If you lie to someone you can be said to be telling them "cr*p" which also means "rubbish". I've also heard "to feed someone cr*p" meaning "to lie".
In the context above, it sounds as if the plan is going to be something unusual and hard to believe so before he even starts speaking, Barney tells Ted that what he's about to tell him about the plan isn't a lie.