My more recent challenge has been transitioning from boundary (ie. "Sorry, thanks for the offer, but I would feel uncomfortable to be there.") to detached (ie. "aw, man... thanks for the invite, I already have plans. Have fun.")
I'm close, though... I think it's more a case that I forget to say that, rather than actually feeling that...
But it starts with working through our emotions and bettering ourselves effectively, and through that, beginning to detach emotionally using boundaries if necessary...
