This is an intense anal stimulation. The first person shoves a handful of olives up their ass and shakes around a bit. The second person puts their lips up to the persons butthole and sucks them out one at a time. Green or black olives will work for this. If you want to be crazy, use both. Eat the olives or save them to use on the other person.
My girlfriend and I went through a whole jar the other day doing the anal olive.