YouTube served this up for me: a woman re-enacts the hilarity that ensued when she attended a Christmas party and did not get the memo as to the attire.
Even I probably wouldn’t show up to a Christmas party in overalls, unless I was specifically informed it was super informal or I knew the venue was a place like a local sports-bar watering hole. But I don’t necessarily think that overalls have to be super-casual! You can dress them up and make them a bit classier, if need be. But don’t take my word for it! Here’s a fashion vlogger who shows the way: