To have sex. Bone = to have sex, ie. act of using one's boner. Sesh = shorthand for session. Usually preceded by some level of makeout sesh.
John: Yo dude where'd you end up last night?
Mark: This chick's place. Had a pretty serious bone sesh too, once we found a condom.
Mark: This chick's place. Had a pretty serious bone sesh too, once we found a condom.
by The Triple Word Store May 16, 2012