The outfit is not the problem. A woman asking whether a dress is too short for a Friendsgiving that includes her boyfriend's exes has already handed those exes a power they were never owed, and the only correct answer is to wear what she planned and stop auditing it. The dress she already owns is fine. What needs adjusting is her relationship to the room, not the hemline. This is the same instinct we traced in Two moods, one muse: choosing between quiet statement and softer ease, where the choice between a quiet statement and softer ease was never about which one pleases a crowd, and in Unfastened Details and the Poise of Dressing Untethered, where the unbuckled shoe carried more confidence than any perfectly fastened one.
Here is the practical read. A hibachi chef and an open bar make this a standing, eating, leaning-over-a-hot-griddle evening, not a seated dinner where a short dress gets to behave. So the question worth asking is not whether the exes will think it's too short. It is whether she can crouch by the grill, hold a drink, and laugh without thinking about her hem once. If the answer is yes, wear it. If the answer is no, the dress stays home, and not because of anyone else in the room. Comfort is the accessory that reads as confidence from across a fire pit.
The exes are the least interesting variable here. They are his history, seated at a table she was invited to, and treating them as judges turns a festive evening into an audition she never signed up for. The women who handle these rooms well do it by being warm, brief, and entirely uninterested in competing. Ask one about the hibachi, compliment the host, keep her hand in her boyfriend's and her attention on the people who matter. Presence does the work that a hemline cannot.
One detail to watch: whether she mentions the exes to him before the party, or lets the question sit quietly until it grows teeth. The dress decision takes ten minutes. That conversation is the one that decides how the night actually goes.