SLIIF Share definition Flag an abbreviation for “so lame it isn't funny” can also be said as “this is so lame it isn't funny” boy #1: and that's why the chicken cross the road boy #2: fuck! that was SLIIF! SLIIF by jai614 April 30, 2006 0 0 Get merch Get the SLIIF mug. Buy Now — $32.95 See more merch