From my perspective, that would’ve been something to see (as well as write about in fanfiction) right there. Plus, Mr. Maclay would’ve learned the hard way about why Buffy was the Slayer as well..

Buffy: (to Mr. Maclay) Do you know what a Slayer is?
Mr. Maclay: Actually... no.
Buffy: Well, as my Watcher Giles puts it, in every generation there is a Chosen One. She alone will stand against the vampires, the demons and the forces of darkness. She is the Slayer.
Mr. Maclay: Really? (Buffy nods, giving him a stern look) Wow. I had no idea.