The purpose of that introduction is buying time to clear out such bad chemicals, so I can express myself in a positive way about something that ticks me off. We'll see how well I succeed. Here goes.
In the matter of inspirational emails, youtube videos, funny images, etc. that we share with our friends, I wish others would extend to me the same courtesy I extend to them. Whether I've seen the forwarded whatever-it-is never, once, or a thousand times before, I smile to myself and sincerely thank the sender for thinking enough of me to include me in the distribution. I never say something like "Oh I've seen that before. It was funny then, too." The sender doesn't need to know if I've seen it before; so far as I can see, my communicating that fact adds nothing useful to the conversation. The sender's intent, I assume, is to share a delectation, a gift. I hope to respond in the same spirit, rather than to my ego's infinite reflections of itself as a sophisticated dudette to whom nobody can contribute anything because I've already experienced it all.
So what if I've seen it before?!? The sender doesn't know that and might, as a result of my response, experience an episode of fear, loathing, and/or embarrassment at having inflicted it on me. That's certainly what happens to me when I get the "Thanks-for-forwarding-that-I-saw-it-ten-years-ago" response.
Earlier today I forwarded an item (to others about whom I care) that I thought was thrilling, spontaneous, and beautiful--it made me feel ebullient and grateful to be alive. I wanted the others to feel that way too. One recipient gave me the seen-it-already brush-off. Now I'm annoyed and my feelings are hurt.
Clearly, I didn't buy enough time and I'm over-reacting. The bad chemicals haven't quite cleared out. I'm going to go over into my corner and grumble until they do. I'll get over it, but I surely do wish I weren't so susceptible to the thoughtlessness of others.