> How do you achieve that?
Hard metal, moderate vertical pressure, drill bit seizing deep in a hole. The remainder of the drill then has to absorb the energy in the gears and the motor, if the drill is hard enough it won't flex but it will break, and if you're unlucky it will break apart in many small pieces.
Eye protection is a minimum with any drill, long sleeves won't hurt. Setting things up so that if the bit shatters it is not going to have anything critical in the plane of rotation helps as well. I've had this happen only twice over 30 years but it's a pretty good surprise when it happens. Both times it was with large bits (20 mm and up), cutting oil and a deep hole in hard steel. That seems to be the perfect recipe. Even then the usual outcome of the bit seizing is the drill circuit protector kicking in before anything bad happens.
The large diameter means you'll be gearing down a lot in the drill so there will be a lot of torque available and as long as the bit is cutting you don't really notice that. I suspect that if you analyzed the problem in detail you'd find that some chip got wedged between the drill bit and the hole walls which would shorten the length of bit available to absorb the excess momentum.
Extracting the remainder of the drill from the hole can be quite an interesting challenge all by itself.