Quoted from usandthem:
Lennon readily admitted in interviews that when he was younger, he hit women. He said that when he couldn’t find the words, he’d hit. In “Good Morning, Good Morning”, the lyric was almost “Time for tea and beat the wife” instead of “meet the wife”. He also wanted to say “Baby, you’re a rich, fag Jew” instead of “Rich man too” (as a statement about their manager, Brian Epstein). He could definitely not be a nice guy at times. A lot of people near him admitted that.
He did a lot more than that. He used to make fun of mentally handicap people right on stage. McCartney said it was because he didn't know how to deal with his fame, but even when he was young, he would make fun of war veterans who were disfigured or people who had handicaps. I always am amazed at how people associate his name or face with "global peace". His own son (Sean) said that he learned over the years his dad didn't have too many friends outside of McCartney.
Still, he was a saint compared to others like Miles Davis. And he did seem to be start to realize the error of his ways towards the end of his. He didn't deserve to go out like that.