I have been struck down by an awesome plot bunny that needs to be written, like, yesterday. Only I'm not writing as much Buffyverse as I used to, so I'm giving it up for adoption.
Here we go: Okay, so, Angel was a bit of a whore when he was human right? Well, I thought it would be hilarious if one of his "fun nights" ended with him impregnating, like, the chemist's daughter or something, but he never found out because next night? gets turned into a vampire. So, centuries pass and blah, blah, blah. Angel hits Sunnydale and OMG does that Xander kid annoy the fucking hell out of him. Seriously, wtf? Well, things happen, and OMG turns out Xander is the direct descendant of Angel's child, which makes him his great-great-great-great-great-grandson or something, I dunno. But we all know Angel, the pathetic dork that he is, he's got to be all "fatherly" now, especially when he finds out that Xander's father is kind of an asshole, which Angel wonders might be hereditary because he kind of reminds Angel of HIS father. Creepy thought, that.
Shenanigans ensue! Xander calls Angel GRAMPY just to piss him off. And this can so easily be twisted into some Spander happening, because what better way to annoy his Grandsire then go after his great-great-great-great-great-grandson?
This needs to be written, people. So I offer it unto you loverly folk to with it what you will. :P