Think this is what american refer to when they talk about a "hostile work environment" in court cases.
I worked somewhere similar- Chief Exec indulged in some very laddish behaviour and it set a tone. Christmas party was one of the occasions it was totally obvious (I'd been there since September).
They were slipshod on some other things too- kept getting taken to employment tribunals over things (lack of confidentiality a common one) and it was only a matter of time before someone filed a serious sexual harrassment case and won, given the behaviour. So, CEO behaviour did encourage others and it did show an attitude of flagrant disregard for the law/common decency which crept into other areas, so IMO you're not wrong to take this into account when assessing whether this is a suitable work culture for you, long term.
I don't think you should quit tomorrow, but start looking for something better. I was out of there by the May after the Xmas party. also keep a log of anything that happens to you, or that you witness happening to someone else, in case you need to demonstrate a pattern at a later date.
IME if you have a good HR department that is internal to the firm you have some hope that this won't get out of hand on a day to day work level- if the HR are people are professional and have some power internally they will keep things getting out of hand for fear of being sued if nothing else. But if HR is outsourced or they are toothless/ a bit amateurish, then this could multiply quickly. if your HR dept is really good, you could to someone there and ask for advice on how to feel more comfortable/what is best to do, confidentially, without mentioning names at this stage. They'll be aware that smething is up inthat department then if anything comes up in the future.
When I left, I had an informal exit interview with the CEo as we were on reasonable terms (he wasn't a total dick, just didn't realise he made other people uncomfortable and that his behaviour set the tone firm wide). He'd spoken to me in the past about working somewhere himself where the Chief Exec. took a very anti-sexist line and the male employees couldn't refer to female employees as girls for example, and how it made the male employees really uncomfortable and nervous. So at my interview this was something I spoke about, I mentioned a couple of things male employees had said, their directly to me or to/about other women in my presence, in a "did you realise this happens" sort of way rather than a complaint. He said "I've let it go too far in the opposite direction haven't I?" Just nodded and smiled.