He actually mentions this on his new album in the song Auntie Diaries, which is about him learning to understand his trans aunt and cousin. He uses gay slurs throughout the song as an example of what he'd say when he was younger. There's a very poignant moment I'll paraphrase:

"I said those words but I didn't know any better. I was taught that words were [just words]." - Kendrick

"Kendrick, ain't no room for contradiction. [Let's look at it from a different perspective]. F* F* F* we can say it together, but only if you let a white girl say n--" - Cousin who's trans