I suggest your person tell you every time when it's egg shells, right away, early so it can be nipped in the bud quickly. Then you both have to decide was it big or small or nothing and solve accordingly.
I told mine when she would vent about a taxi driver or store clerk, etc.. that not everyone has the best day every day and it's not a big deal, after I agree first. Again this didn't happen often but the pattern was easy to spot. She even jokingly called herself a cranky toddler when in this state which I lovingly and jokingly would say later on as a warning for her. Humor helps a lot. Getting the infj to be less serious and laugh especially at oneself was very valuable.
For you, the infj, I would sit down with a friend or someone who knows and has seen the egg shells and you could get a better understanding to be able to recognize it in yourself so that you can better decide if your acrions or responses are appropriate for the events or situation.
Early direct communication, in person helps most.