talk out (the side of) one’s neck
v. phr.— «Only the sum of all these experiences would be able to make up Universe itself. of course i’m just “talking out of my neck” as we say in Dutch.» —“Synergetics—jitterbug, scale” by Gerald de Jong Usenet: bit.listserv.geodesic Dec. 3, 1994. (source: Double-Tongued Dictionary)
Further reading
The word filibuster has a long and colorful history, going back to the days when pirates roamed the high seas. Today it refers to hijacking a piece of legislation. Plus, the language of yoga teachers: When doing a guided meditation, you may hear...
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...