SIILF Share definition Flag SIILF. Sister in law id like to fuck. I have no idea why Tom married Sarah. She's such a dog. I don't get it. All three of her sisters are SIILFs. SIILF by Mega Hemroids October 2, 2017 0 0 Get merch Get the SIILF mug. Buy Now — $32.95 See more merch