I too, am a pretty non-confrontational person and will rarely tell someone to go to hell. But that doesn't mean that boundaries can't be set in different ways. I just haven't figured out how that is done when it is my boundary. "No", works well, but I do always want to give a reason. Of course, there has been campaigns (related to other things) - "No means no", so if for those other things, it means "No", then why cannot it not for a mundane person like somebody asking for a donation to charity outside the supermarket?
I am too often waylaid by those types. Sure, they're just doing a job, but I want my "no" to be taken seriously, not for "objection handling" and the other little bits of language-psychology to try and scrape away at that fortress of my own choice and to try and get an outcome that I don't want.
Telling someone to go away, no, or more satisfyingly, to "get fucked" is a powerful agent of our own freedom. But, unfortunately, it isn't that simple. I want to bring semantics into it, because I always like to bring semantics into things.
"hell" is, of course a concept, but if we are going to capitlise it and make it a proper noun, we're doing something more powerful - we're admitting that the three headed dog at the end of the river styx (I know I mixing mythology) here - is real, and that a whole lot of other made up stories are real too. :P
I went to university alongside a very smart girl. She went to a religious school. She wrote a science paper on how "hell" must be real, because the Earth's centre is warm, making "hell" an exothermic place.
But back to saying "no", and closing off the boundary, and erecting a fence: there's always going to be a glimmer of the "what if" in your internal monologue, but I feel that instead of ascribing value to that part of the inner monologue, perhaps it should be "What if I let go of this earlier?"