An indescribable act, feeling, or moment. Also can be simply hitting knees with another person as a friendly gesture in the place of a handshake, fist bump, or high five. It has lately evolved into just a loose term.
Jordan was overcome with the bam kneez!!
Mindless dude #1: Yo dude!
Mindless dude #2: (pointing at Mindless dude #1 with both hands) Bam Kneez!