I doubt they'd need the word "coffee" to infer what's happening when said message gets sent. Who sends it and to whom would be just enough thank you very much...
And they'll know who you contacted and when. That allows for a lot of things to be guessed. Especially with hundreds of thousands of messages per user available to them.
Yeah, but my ISP has to follow the local laws and I can easily switch ISPs if I dislike my current one. Try that with Facebook.
Yeah, I might use a VPN but I'd also have to force all my contacts to use one as well.