First referenced on the Steve Dahl/Gary Meier show on WLS in Chicago in the 1980s, it refers to one or more people bathing an individual using only their (human) tongues as the washing/cleansing agent. Hence the name.
"Pardon me, but I must be going; my manservant David has arrived to give me my weekly Japanese tongue bath."
by Reacharound McGillicuddy June 17, 2013