I'm thinking two things along these lines.
There is scientific evidence that women metabolize alcohol differently from men, and usually it is stored in adipose fat (if i'm remembeiring correctly), so essentially it "makes you fat" (vague over simplificatiton). But, it will definitely derail the diet.
Next, i think that when a cheat coincides with a TOM, the "cheat" becomes the "two week habit" until the hormones flip and *bam* no longer interested in that cheat. This is what I observed in myself at least. Here was my process:
Cheat: Friend brings in tacos with white tortillas; I love tacos! I eat tacos!
Cheat step 2: TACOS! I CRAVE TACOS!
Cheat step 3: MUST EAT TACOS.
Cheat step 4: WANT TACOS, will not eat due to PB!
Cheat step 5: WANT WANT WANT TACOS -- eat PB BAS with taco flavors. Body tells you to go to hell you dirty liar as those were not TACOS and I DEMAND TACOS.
Cheat step 6: TACOS! TACOS TACOS TACOS TACOS.
Cheat step 7. Menstruation begins. TACOS WOMAN! TACOS!
Cheat step 8-11: MUST EAT ALL OF THE WORLD"S TACOS.
Day 12. What are you talking about? tacos are disgusting.
Now, if my friend brought me tacos at any point during the estrogen phase, I'd be like "no thanks." or I'd be able to have one and move on with my life. Yay! 20% PB is easy.
But if i'm post ovulation, forget it. MUST EAT ALL TACOS.