Jeff: "I'm sorry Dave, I just can't make that kind of commitment. However, if we do happen to be best friends in the afterlife, I'll definitely upgrade our relationship."
Dave: "Thanks man. I really appreciate it."
"Yeah, he's my bffl."
"Best friends for Life"
Either used to mock shortened computer lingo as in "omfg we are sooo bffls!" or mistakingly said when referring to a friend, can slip out in coversation by accident like LOLs sometimes do.
Mary: Oh god no we bonded in the ladies room the other day and are totally bffls!
"Omg Stacey and Lindsey are like joined at the hip .. they are like over the top bffls!"