There's the argument to be made that it doesn't matter WHAT you say so long as it's in the moment and you're hot for the other person, but I say this is horsefeathers. Some stuff you just should not ever say to someone.
The hot second you indicate to a dude that you think threesomes are sexy and might, in the absolute RIGHTEST of right circumstances, be open to maybe sort of VAGUELY considering having one or something like one, they will never, ever shut up about it.
Last week, we came up with a whole slew of terrible things dudes have said to us in bed. But as someone who has said some weird fucking things while naked, I have to say it's easier than it might sound.