If the office Christmas Party goes really traditional and you end up making 'cheeky' photocopies, you won't be exposed to toner or harmful light for long enough to hurt you, but you may well find yourself spending the rest of the evening face down in casualty, having shards of glass removed from your bottom. This is a surprisingly common occurrence, as photocopiers simply aren't designed to be robust enough to take any kind of weight.
The same goes with most other office or workplace equipment from staple gun shoot outs, paper-opener sword fights to re-enacting the French Revolution with the office guillotine. It goes without saying that items of work equipment are not toys, but in drunken hands, even fairly innocuous devices can turn seriously dangerous.
Hold the office party somewhere which is suitable for people to let off steam and have a good time. If it has to be in the office, then make sure that where possible everything is locked away or switched off, including the computers (to stop abusive messages being sent that people might regret, or Page 3 sites being logged on to).
Never hold the party in a workshop, a warehouse or similar premises, there are just too many accidents waiting to happen - and though the majority might be minor, it's not worth the risk.