Possible interpretations: Remember the Qur'an is a teaching revelation from God using parables and allegorical stories and this story of Joseph is about sin and going through trials then redemption and God giving you blessings after your trials.
The lesson is Pharaoh's wife was so in love infatuated with Joseph and his good looks, that she didn't even know that she was harming herself; would lose everything even might get herself killed because of her lust, sins, she's willing to lose everything just for this sin of adultery or lusting after another man, when she's married, the banquet also teaches that even these other women would harm themselves without knowing it, even cutting themselves because of their sins adultery lustful behavior then realize they were harming themselves only for lust, these women even glorified Allah while sinning lusting after Joseph harming themselves while glorying God.
This is the teachings, it's like a drug addict, they are only harming themselves but don't realize it, until it's to late.
Joseph rejected this sin and wouldn't harm himself putting himself under danger from Pharaoh and Allah on judgment day, his choices were righteous, so there's no lesson about Joseph harming himself like for example grabbing this women and accidentally braking something and cutting himself as a parable of what could've happened to him, in the future when caught by Pharaoh and then tortured by Pharaoh just because the choice to sin over sexual lust when he could've just married a single beautiful woman; even more beautiful this this married woman and wouldn't have these problems.
It's also possible this was her hearing their gossip telling everyone about her to the people thus shaming her, she tells them when he comes out if he's not incredibly handsome and you lust after him like I did even willing to sleep with him cheating on your husbands, you will cut yourself or I will cut you, so her anger learning about this gossip she's getting back at them because of their gossip about her in the streets, this is possible because she obviously wasn't a good woman with moral laws but probably evil and vengeful: this is the real world and these people weren't very nice in those days and even today, so it's possible she was getting even with these women because of their talk.
Notice she's hearing about their slandering's and invited them to this banquet and gives them knives to get revenge and stop their slandering her.
So when she heard of their accusation, she sent for them and prepared a banquet for them; she gave each one of them a knife (to cut the foodstuff with), and she said [(to Yusuf (Joseph)]: "Come out before them." Then, when they saw him, they exalted him (at his beauty) and (in their astonishment) cut their hands. They said: "How perfect is Allah (or Allah forbid)! No man is this! This is none other than a noble angel!"
When she heard their slanderings, she sent for them and prepared a banquet, and gave each of them a knife (for paring fruit), and called (to Joseph): "Come out before them." When they saw him, the women were so wonderstruck they cut their hands, and exclaimed: "O Lord preserve us! He is no mortal but an honourable angel."
I don't think this King of Egypt wife wouldn't like these other wealthy women spreading her adultery in the streets and probably invited these women to a banquet then threatened them with harm if after seeing Joseph didn't cut themselves otherwise she would do it for them getting even with them, this is very logical and possible instead of this being a supposed distraction and a accident but she's deliberately giving them knives, so there's some sort of revenge going on, Allah knows best.