I personally would never build a guitar that:
- is pointy
- is neon colored
- is gold or silver
- has a flake finish
- has a band's graphics all over it... I don't really get that unless you're in a cover band or something.
- has crazy inlays everywhere
- has a huge ugly whammy bar bridge
- has gold hardware (probably not... some builds look good with it, but 95% don't need it)
- has black hardware (metal should look like metal in my opinion)
- has plastic black or cream inlays
- has a shell pickguard on anything but solid paint
- has more than 2 humbuckers (or humbucker size) pickups
- has relic'ing... just wrong. It's cheating.
- is a Jagstang or a Mustang
- has a huge baseball bat neck because I can't reach anything on a neck like that
- use a Jazzmaster/Jag trem bridge. I'd like to build a Jag or a Jazzmaster, but it will not have the traditional bridge.
There are lots and lots of things I would never choose, really. I don't think they're guitar building blasphemy necessarily, I just wouldn't do them. Except Jagstangs, those are blasphemous.