Of course, I usually get yelled at for offering my two cents on a DM's house rules. But I make the effort anyways!
Like in a desert survival game, the DM had us acquire "resources" that would be depleted as we traveled across the desert, such as food, water, shelter, what have you. Knowing full well that there were spells that could obviate this fact, he just gave you bonus resources for unspent spell slots whenever you took a long rest (but to take a long rest required a cost of resources).
Immediately, I noticed something he didn't take into account- on days where there were no encounters, spellcasters would have their full allotment of spells. I tried to point this out, but the DM just said "damn it, James, can we just playtest this without you poking holes in everything?"
Ok, sure thing. I just quietly marked down how many resources I generated each traveling day, and where they came from (Survival checks, unspent spell slots, etc.).
When we got to our destination, he said we could sell off unused resources for gold. I made the adjustments, and started my spending spree at the local bazaar.
"Wait, where did you get all this money? You didn't find that much treasure!"
I gave him my notes and watched his face pale, then turn red. "Why didn't you tell me this was going to happen?!"
"I tried, and you told me to shut up!"