Rhubarb pie - halve the sugar & don't use that wimpy pink stuff that's forced in greenhouses, get the big old fat green stalks about an inch thick that grow naturally, for a much stronger hit.
If that's not enough, try adding sloe berries… or just eat the rhubarb raw, or dipped in lemon & vinegar.
Ahh… childhood. We used to grow it in the back garden & it was a notable source of savage amusement in late summer.
Another savage amusement was sherbet lemons dipped in alum - I wouldn't recommend this to anyone over 12. The amusement value palls as an adult, though I suppose you could wash it down with a big red wine.