Rude isn't a term I would apply to deciding who I allow to have any given sexual practice with me or not.
I am fluid bonded with both partners. However-neither of them have any other partners and being fluid bonded may change if that status changes. It's my body-my choice to say no. Likewise-either of them could say they no longer want to be. That's not rude-it's reality. Personal preference and that activity requires both parties to be ok with it.
"Love As Thou Wilt"