Especially when readers don't know my relationship to the subject matter, or my relationship to the individual I'm addressing.
To your point about relevance, I'm going to point out to you that zero people are actually advocating banning a word. They're saying "hey let's stop calling girls who express leadership skills "bossy" because that has negative consequences". To which I think the average person would probably be open to. They are advocating not using a word in the wrong context. Call kids bossy when they're being brats, sure, but when someone, particularly girls are being leaders and doing the same things that boys are complimented for, don't call them bossy.
#WhenSomeonesBeingALeaderDontCallThemBossy is a pretty long hashtag and a terrible way to quickly market your campaign. #banbossy is memorable, gets to the point, and can encourage a conversation.
"I fail to see how the lyrics from a Jay-Z song from 2002 are anything other than completely irrelevant to the Ban Bossy campaign."
We're talking about banning words. If I had to guess, I'd bet more people would support banning "nigga" than they would "bossy". Personally, I don't think any words should be "banned" because it's simply not possible. Society may evolve to not use a word, or shun those that do use a word - but a campaign to "ban" a word does an injustice to the literal meaning of the word "ban" because it's just not realistic, or possible.