The phrase someone close to you says before they point out a flaw, something you did or are currently doing wrong, a mistake you made, something embarrassing, or something just flat out mean. This phrase is mostly used by parents and spouses, not so much by close friends and non-immediate family members.
Mom: Jerry, you know I love you, but you did a really shitty job at sweeping the kitchen floor.
Jerry: Ugh you always say that before you yell at me for something stupid.
Dad: Allan, you know I love you, but that haircut you got today makes you look very homosexual.