The Celebration

Respected family patriarch and businessman Helge (Henning Moritzen) is celebrating his 60th birthday at the family-run hotel. Gathered together amongst many family and friends are his wife Else (Birthe Neumann), Christian (Ulrich Thomsen), his sullen eldest son, his well-traveled daughter Helene (Paprika Steen), and Michael (Thomas Bo Larsen), his boorish younger son. Christian's twin sister, Linda, has recently taken her life at the hotel.
Before the celebration dinner, Helene finds Linda's suicide note, but hides it in a medicine bottle after becoming upset by the contents (which are not revealed to the audience). Michael fights with his wife, whom he had earlier abandoned on the roadside with their three children, and then has sex with her. Michael later is pulled aside by a waitress with whom he had an affair (and had made pregnant) and then beats her when she disparages Helge. Later, during dinner, Christian makes a speech to the family in which he accuses his father Helge of sexually abusing him and his late sister Linda. There is an initial shocked silence, but the party gradually returns to normal, as the guests react by silent denial. In a private conversation in the pantry, a seemingly baffled Helge asks Christian about his motivations for slandering him, and Christian appears to recant his accusation. However, Christian is spurred to further action by hotel chef Kim (Bjarne Henriksen), a childhood friend who knows about the abuse. Christian then stands up and continues his toast by accusing Helge of causing Linda's death. Helge speaks to Christian alone and threateningly offers to announce in a toast Christian's troubled personal history, impotence with women and his perhaps inappropriately close relationship with his late sister, Linda. Christian says nothing in response to the threat. Further exacerbating the tensions of the day, Helene's black boyfriend Gbatokai (Gbatokai Dakinah) shows up, enraging the racist Michael who later leads most of the partygoers in singing the Danish song "Jeg har set en rigtig negermand" in a racist way to offend him. During a toast, Else makes a series of back-handed compliments towards her children, accusing Christian of having an overactive imagination as a child and asking him to apologize for his earlier accusation. Christian responds by accusing her of interrupting Helge during one of the rapes, yet not interfering with the incident, and calling her a "cunt". Michael and two other guests violently eject Christian from the hotel. When Christian walks back in, they beat Christian and tie him to a tree in the nearby woods.
Christian unties himself and returns to the house. Helene has a headache and asks one of the waitresses (Pia) to go and fetch her pills. Pia finds Linda's suicide note in the medicine bottle and gives it to Christian. Christian gives the suicide note to Helene and leaves a note with the toastmaster. The toastmaster reads aloud the note that urges Helene to read the suicide note to the guests. Helene does so. Linda's note states that she decided to kill herself after feeling overwhelmed by dreams in which her father was molesting her again. In a fit of anger, Helge admits to the abuse in front of all the guests by saying that it was all Christian was good for. He then leaves the dining room with the guests stunned. Christian, who is drunk, faints after walking out of the dining hall and imagines seeing Linda. When he awakes, he learns from Helene that Michael is missing. We learn that the drunken Michael has called Helge outside and then beat his father severely, promising him that he will never see his grandchildren again.
Next morning shows the family (excluding the parents) and guests eating breakfast nonchalantly. Then Helge comes in and speaks to the group admitting his wrongdoing and declaring his love for his children. Michael coolly dismisses their father from the table, stating that he should now leave so that they can have breakfast. Christian reveals that he is going back to Paris, and asks Pia (who has known Christian for years) to accompany him.

Question: Why does Michael beat the waitress?
Answer: She puts down on Helge.