AITA for banning my cousin after he disrespected my home and my relationship?

A 25-year-old man lives with his girlfriend and is temporarily letting his younger brother stay after a layoff. They invited their polyamorous cousin over for a nostalgic dinner featuring their late grandmother’s recipe. The cousin arrived alone (his live-in partner had plans) and immediately began openly flirting with the girlfriend — touching her body, complimenting her perfume, asking sexually explicit questions about the boyfriend’s performance, and later poking at her thigh tattoo.

The boyfriend pulled him aside and asked him to stop. The cousin dismissed the request, saying he “doesn’t respect exclusivity” and calling the boyfriend controlling. When the behavior continued, the boyfriend kicked him out. He now plans to ban the cousin permanently from their home, but the brother says the flirting was “too minor” and that he should respect the cousin’s poly beliefs. Is the boyfriend the asshole?

‘AITA for banning my cousin after he disrespected my home and my relationship?’

The dinner started with good intentions:

The flirting began almost immediately:

The boyfriend tried to handle it privately:

Touching someone’s body (especially thighs) without consent, making sexual comments about their partner, and continuing after being explicitly told to stop is sexual harassment — not “flirting” and not excused by polyamory. Polyamory requires enthusiastic consent from everyone involved; it does not grant blanket permission to pursue anyone regardless of their relationship status.

The cousin’s line “I don’t respect exclusivity” is gaslighting and entitlement. Respecting someone’s relationship structure is a basic social expectation — just as monogamous people are expected not to hit on poly individuals in committed group dynamics. The boyfriend’s response (private warning → immediate removal after violation) was proportionate and appropriate for his own home.

The brother’s opinion (“too minor,” “respect his ideals”) is irrelevant — it is not his house, and he is a guest. Defending the behavior while living rent-free adds an extra layer of entitlement. The girlfriend’s comfort level should have been the priority; her non-intervention does not equal consent or approval.

This is not about “poly vs. mono” — it’s about basic respect and consent in someone else’s home. The boyfriend is not the asshole; the cousin is. Banning him is a reasonable boundary.

Check out how the community responded:

Almost every commenter agreed the boyfriend is NTA — the cousin’s behavior was disrespectful and inexcusable regardless of poly beliefs:

The boyfriend bears primary responsibility for the ruined day. Knowing fulmars defend their nests by projectile-vomiting foul, burning oil — and knowing his girlfriend is easily grossed out — he had a duty to provide a clear, specific warning rather than a vague “stay far away, they get angry.” The term “far away” is subjective, and 15 feet proved dangerously close.

Deliberately withholding the disgusting detail to spare her feelings backfired, causing far greater distress when she was drenched in vomit. While the girlfriend could have asked follow-up questions or maintained greater distance from wildlife, she relied on his prior knowledge. The failure to communicate fully and accurately rests mainly on him. A sincere apology and shared laughter afterward would have salvaged the vacation more effectively than defensiveness.