My buddy wanted a 20 sided with "Fuck you " on the 20 and “fuck me” on the 1 face.
I could not find that, but on Amazon I found a single D20 with “fuck” on the 1 face.
I assume we all know what the singular of “dice” is?
Do not Google “fuck die”. 
[Moderating]
Moving to the Game Room.
[Not moderating]
One of the members of my D&D group has that d20. I’ll see if she knows where it came from.
According to the Collins English Dictionary,
A dice is a small cube which has between one and six spots or numbers on its sides, and which is used in games to provide random numbers. In old-fashioned English, ‘dice’ was used only as a plural form, and the singular was die, but now ‘dice’ is used as both the singular and the plural form.
Obligatory ‘Fook Mi’ and ‘Fook Yu’ Austin Powers clip. Probably NSFW due to the audio pun and sexual implications, so in dropdown:
Of course, in my gaming group, we went with a Futurama clip for 20s/1s.
Oh, cruel fate, to be thustly boned! Ask not for whom the bone bones, it bones for thee.
Best of course if it happens after you’re forced to escape without all your swag/loot!
Yeah, per your own cite it will depend on you’re talking about American or British English. In Britain, “dice” is both singular and plural, while in America “die” is singular and “dice” is plural. (Which tracks for me, as an American, I’ve never heard or read “dice” used as a singular form despite being a tabletop gamer for 40+ years.)
Back to the OP:
I can find a lot of companies and Etsy vendors who will put a custom imprint on one face of a d20 (either on the “1” face or the “20” face) – what a few minutes of browsing, unfortunately, doesn’t seem to show me is a company which will custom-print both of those faces on the same die.
I think this place might work. Looks like you can customize every facet on the die
Interesting, thank you.
Or you could go to the link in post 4, which has exactly the product the OP describes.