A phrase that emphasizes that one is speaking very truthfully or stating a fact in which he truly believes. Literally means that the person would bet his life on the validity of the statement.
"Gotta keep ya cash coming and that's on my life." -Ja Rule, "Wonderful"
"Suge Knight's a bitch, and that's on my life." -Snoop Dogg, "Pimp Slap'd"
"I pissed on your 12-year-old daughter last night, and that's on my life." -R. Kelly, "Your Daughter Drank My Piss"