Poor Spike, the downside of getting older😀 I can see him being this annoyed with this situation and Buffy teasing him and totally enjoying this.
I've always assumed that since William needed glasses, Spike does too (Dalton wore them even in vamp face, after all!) That's why he had trouble reading Giles's handwriting when Dawn had no problem with it. He's just too vain to admit it. :D