what happens when I put in three 100 watt bulbs in a standard ceiling fixture?

60 watt incendesent. now why not get smart and if you need it that bright which i know of many reasons why go with a florecent 100 watt screw in bulb you wont be damaging the fixture or be causing that premature aged look on the ceiling l.e.d. as far as i have seen just have that one lumen output. and them florecents you got colors the warm white hue the cool bluish white and the warm yellow similar to the incandecents. sure they cost a tad more but over all they last longer and use way less power to light up the room. (as i glance at all of mine that i have lit)

All lighting fixtures are required by UL listing and most codes to have a 90 degree centigrade rating. That is to say that they must be able to withstand a certain temperature internally when USED WITH THE PROPER EQUIPMENT. Seriously though, you'll probably just cause a thermal overload and the thing will shut off until it coold down. That is also assuming that it's a newer fixture and not something that grandpa installed right after the War. Go by the rating, please, for the sake of the fire department.

Possibly nothing. Possibly overheating the sockets to where things scorch or melt. Possibly starting a fire up in the ceiling if the fixture is up tight against it.

Rules exist for a reason. Break them at your peril.

It will overheat and the hot fixture could ignite any combustible materials in the vicinity.