Not only have I read a Scalia opinion, I wrote a lengthy case note on Scalia's dissent in Romer v. Evans to satisfy my third year writing requirement. It was less a matter of pretzel logic and more a matter of basing the entire opinion on an invalid (in that case, bigoted) premise, then applying consistent logic to form a pre-determined conclusion. His premise was to employ the old world definition of homosexuality: that being gay was defined by having anal sex, not by having a same-sex preference. That was the problem. His actual logic was fine if you bought the premise.
I haven't seen any bad SCOTUS decision yet which would compare to concluding that Medicare is Constitutional for one age bracket of Americans but not any other age brackets. I'm not even sure how they would attempt to frame such an argument.