In reply to Afro:
> has anyone ever managed to break a hold indoors?
>
> i dont just mean making it spin around the bolt, but a part of it actually breaking off?
>
Many times, both climbing and setting.
> this happened to a mate of mine recently and left him feeling like a tool as we joked that the wall would have to implement a weight limit, but bizarely, he's not that heavy... there were several other climbers there that day who must have been heavier that him
I weigh less than 10st, weight is not a problem. Holds will break typically around the bolt hold if: 1) they are old, and have been placed/removed quite a lot (i.e. resetting); 2) they've been overtightened during routesetting. I used to do this more with bigger asymmetric holds, since they need a bit more torque to stop them from spinning; 3) using the wrong type of bolt. Some holds have chamfered bolt holes, and using a square bolt will weaken them.
In summary, it's really not your mate's fault at all. It happens.
>
> it made him climb pretty gingerly for the rest of the day though
Probably good for his technique then