Other than my recent Boeuf Bourguignon debacle two really EPIC fails come to mind.
I was in my early 20's, a new bride (first marriage) and wanted to cook dinner for my parents and in-laws. I decided to make a chicken and sausage gumbo. I REALLY thought I knew what I was doing. As the eldest of 7 children I assisted my Mother in the kitchen for years. The operative word is assisted. I chopped and diced and stirred and added ingredients at her direction.
I started early in the morning. First I made a dark Roux. Lovely. I seasoned and browned my chicken and sausage. Deglazed the pan. Chopped all of my seasonings. Put it all in my gumbo pot and started cooking.
While my gumbo simmered I cooked my rice, made a potato salad and prepared a French bread with butter, garlic and Parmesan - ready to toast in the oven.
I was SOO proud of myself. I really had it together. I had plenty of time to clean the kitchen, set the table then shower and dress.
Before turning the heat off under my gumbo pot I tasted for seasoning.

All I tasted was roux!! I

.
I was frantic.
I took all of the solids out of the pot. Removed some of the liquid. Added water (I did not know about broths and stocks) . Heated. Tasted. Still too much roux. Repeat 2 more times. Finally - a decent gumbo base. Added everything back to pot and prayed.
It was the worst gumbo I ever made.
2nd Epic Fail
A couple of years later.
A co-worker was a hunter and had an excess of wild rabbits. Click! I can get some rabbits and grill them for my parents and siblings and my husband's parents and siblings. I got 12 skinned rabbits - $1 each.
My only experience with game was eating it. I had NO experience cooking game. Dad and my brothers hunted. Dad cooked the game.
Step #1
Call Dad.
Question #1 How do I cut it?
Question #2 What next?
Dad said to cut it like a chicken then marinade it over night in some vinegar to get the gamy taste out. Rinse. Pat dry. Season like chicken for grilling.
I did as he instructed.
Again very proud of myself.
I had side dishes made. The rabbit was ready for the grill. The family gathered.
My Ex put the rabbit on the grill and -

an overwhelming smell of vinegar!
I
Dad laughed until he
When he told me to marinade in vinegar he meant 2 or 3 TBSP. I used a gallon.
We had take out fried chicken.