A "sparkling water enema", currently popular among wealthy UK homosexuals and bi-curious metrosexuals.
One partner plays the "waiter". He takes a small glass bottle of sparkling Perrier (the narrow sloping-necked style is required). The "waiter" unscrews the cap and places his flat hand over the top. He agitates the bottle and quickly inserts the neck of the bottle into the anal orifice of the "customer".
Clearly, fast action and effective pre-lubrication are required to obtain the maximum effect.
The two product managers took a line of coke each, then gave each other a Perrier.