when two events can occur only in conjunction with one another, i.e. neither one can occur without the other
Legend has it that being a tree-hugger and being a hippie are exclusively mutual.
Liberal: "Being homophobic and having repressed homosexual desires are exclusively mutual."
Conservative: "Hah, that's a good one."
Liberal: "Remember that recurring dream you told me about?"
Tim: "I wanna hook up with Kim, but Stacy's my girlfriend"
John: "I don't understand...those are exclusively mutual aren't they?"
John: "If you break up with Stacy, Kim will be pissed cuz they're good friends. a.k.a. no Kim for you. On the other hand, if you don't hook up with Kim, Stacy will get bored of your drama-lacking relationship and eventually dump you. And then Kim will think you're a loser, and again no Kim for you.
Tim: You are a genius. I'll be right back