Yup multiple times, mainly while trying to learn to balance on the front wheel on my old bmx bikes when I was a kid.

As an adult I watched one of the neighborhood kids take my MTB for a ride up the street. I had just adjusted the brakes to where I like them, short pull, instant engagement. The kid wasn't aware, another kid ran out in front of the bike and kid grabbed a handful of front brake. I have never seen someone go over the handle bars so fast. I felt bad for the kid but it was funny to see.

Last year whislt riding my road bike it mech disc, I came into an emergency braking situation. I knew a turn was coming up and the group was slowing down. So I looked down to grab a water bottle. When I looked up, the turn wasn't the one I was anticipating, it was a road closer. The entire group had slowed and was turning right infront of me and I had the bottle in my right hand. I was able to grab a handful of front brake and fingerful of rear, never went over, and didn't hit the other riders. But it was a very close call, and the pucker factor was extremely high.