Common expectation? Not exactly but I know what you mean. There were nerves about the policy and I still would not have done that bit when they did it, but not because I expected millions of people to abandon social distancing entirely. My concern was for specific chains of transmission, individual spread, local clusters etc. Some people take these ideas to their extreme and expect mass non-compliance and spikes within weeks. The reality is almost always far more mixed than that, and we have mostly only had anecdotal evidence about behaviours over these months. Also we havent really been given much data about compliance in general, press conferences tended to focus on transport figures where it was easy to show a massive and sustained change to behaviours. In fact it is likely that there has been plenty of non-compliance with all manner of rules all the way along. Some of it through no fault of peoples own instincts, but rather the situations they were placed in with their financial situation, jobs, accommodation etc. But in other areas there have been some people 'cheating' all the way through, and compliance has varied by region, age, etc.
I dont know exactly how much of a problem the minority who react very badly to mask stuff will cause. I suppose I expect there will be specific incidents that get highlighted in the news, and some of these will be quite ugly. But no matter how bad such incidents are for the people (eg shop workers) involved, there is a difference between a bunch of incidents and non-compliance on a scale that will force a rethink about how compliance is enforced. When it came to other issues of policing the pandemic in past months, the likes of Hancock would fall back on the rhetoric about 'public consent based policing', which often involved a somewhat hands-off approach. The masks stuff could test that somewhat illusory stance, or it could be dealt with via the usual absurdities and turning a blind eye.