I have 2 really.
Years ago I picked up my first Buzzon Element X. Threw it once noticed on the return it was loosening a little, so I tighten it and check it. Next throw I was doing some longer string work and after about 30-45 seconds the 2 halves completely spun apart and flew 2 different directions. The 1 half cracked in half (with 1 of the halves still attached to the weight ring), the 2nd half got grated like cottage cheese (I was standing on concrete) and the weight ring fell out. The bearing, axle and 1 of the spacers complete vanished (I was throwing outside on the porch and they flew into the bushes). First day I owned it… less then 3 hours after receiving it in the mail from Buzzon.
The other one was a YoYoJam Journey I picked up from The City Museum (where the MoYo States are held) in St. Louis, MO (where I was born and raised). Was outside in the front yard messing with a Yo-Yo while talking to a buddy. He wanted to try one out, I let him use it. Taught him a couple things, and he did an Around the World (and apparently didn’t have the foresight to know about string tension on your FINGER) and it went flying up in the air and landed in the driveway. 20 Feet away. Needless to say there were some pretty nasty gashes and dings in it from the pavement, and the bearing just doesn’t play right anymore. (Replaced it with a Kickside from MoYos this year)
Those are really the only 2 problems I’ve had. Never really gotten any significant damage to any other Yo-Yo. My YYJ Xconvict some how got a crack in it, near the weight rings, after moving across country.