My sister tried to call dibs on a name that I liked (after I was pregnant). Honestly, it irked the heck out of me and thereafter I started telling people not to tell me their names so that nobody felt like I "stole" their name.
My sister has said she doesn't want kids, and even if she does end up having them, who knows if she'll have a girl. I had a boy and have another name that I plan to use for a girl anyway, so it probably won't end up being an issue, but I was pretty irritated by that.
ETA: I think you're allowed to feel annoyed, but I guess my point is that I am team can't-call-dibs.