It's a theory by wealth manager Brent Johnson that the next big recession will trigger an enormous demand for dollars. The dollar will rise against most other currencies and non-US bonds thus sucking up all the liquidity (that's the milkshake part).
He's been on many podcasts to explain his theory and provide updates. I will link you an interview at realvision from september 2020 timestamped at 51:55 where he goes through it in summary: https://www.youtube.com/watch?v=h_HCIyc6MaA&t=51m55s
He's been on many podcasts to explain his theory and provide updates. I will link you an interview at realvision from september 2020 timestamped at 51:55 where he goes through it in summary: https://www.youtube.com/watch?v=h_HCIyc6MaA&t=51m55s