Lockdown house parties among groups who don't live together are the new ultimate sin. They can become scenes for the super-spread of the coronavirus.
People may think they are not doing anyone any harm staying indoors and among their own group of friends.
But it is a perfect breeding ground for the virus.
And a legacy of revelries that were held over the bank holiday weekend may yet be seen in newly diagnosed cases of the infection in two weeks' time.
Gathering people from different households indoors presents an obvious risk. The danger of infection indoors is almost 19 times higher than in open-air environments, according to research from Japan.
If you throw alcohol and a lack of physical distancing by exuberant party-goers into the mix, it is a recipe for transmission of the virus.
As the party revs up, people are more inclined to speak loudly. Raising your voice can leave coronavirus lingering in the air for up to 14 minutes, research has found.
Thousands of tiny droplets sprayed from the mouths of people talking noisily can remain in the air. Add in the odd cough or sneeze and the virus is gaining new hosts.
People are also less inclined to wash their hands as often as they should in this kind of atmosphere.
Young and healthy
The people attending the party may all seem in the best of health and in the case of students feel young enough to have little fear of the virus as it is less likely to affect them.
That may be so and younger age groups have a much lower chance of falling seriously ill with the virus.
However, it is unpredictable and young patients have ended up in hospital with complications here.
We also now know that many people who are well have the virus but are asymptomatic. They are capable of unwittingly passing it on.
When the party-goers go out into the wider world, and more have picked up the virus during the celebrations, they may be going back into their own homes where one member of their family is vulnerable to the infection.
They may go to the shops or travel on a bus, bringing the risk of passing the virus on to somebody else.
The back-garden barbecue is not in the same league as the indoor party, but if people from different households come together and do not socially distance there is a risk.
The current public health advice is that up to four people from different households can meet in the outdoors for a short time while keeping a two-metre distance.
The advantage of the barbecue is that it is outdoors. But the garden would need to be large and if there is a shower of rain there is the chance everyone will rush into the kitchen or living room.
The other problem will be any sharing of plates, knives or forks that have to be brought in later to be washed may have the virus on their surface.
Disposable plates and utensils could solve that issue.
It has become clear in recent weeks that asymptomatic infection here is significant. You can have the virus without symptoms or you could be pre-symptomatic.
In any gathering this summer, it is worth remembering that although somebody looks well, they may have the virus.
It's why we should be wearing face masks or cloths if we can to prevent us passing on the virus.
Day at the beach
According to infectious disease consultant Dr Sam McConkey, being at the beach with other people is "relatively safe". The sun may kill the virus and the wind blows it away.
Gardaí, however, have not been taking any chances and over the weekend moved groups from Dublin's Forty Foot bathing area and they closed off Bull Wall bridge to reduce the numbers gathering at Dollymount Strand.
The restrictions around get-togethers will ease from June 8, when phase two of the exit from the lockdown will come into effect.
It will allow up to four people to visit another household for a short time. Visits to the homes of over-70s and people who have been cocooning due to a medical conditions will be allowed.
More detailed guidance on how to do these safely is expected.
The virus is still circulating and newly diagnosed cases are emerging daily. Over the past week, 500 new cases were notified.
There is less virus around but caution will be needed whatever the new freedoms.
Visiting relatives around the country
Dr McConkey points out that if we restart too soon, widespread non-essential travel from cities like Dublin and Cork to other parts of Ireland, like the west, which have had no recent new cases, brings a risk of more infections.
If restrictions are eased while there are around 20 to 30 new cases a day and people do not know where they picked it up, the risk is that, over five days, infections could double.
Over 50 days, it could rise exponentially to 20,000 cases.
It's a reminder of how soon we could be back to a situation where the spread of the virus is again difficult to control.