Not cooking the turkey long enough on my first Thanksgiving Dinner attempt.
Walking into the kitchen.
ROFL Officer! :D
I tried baking a cake from scratch when I was about 12...if it hadn't been so heavy it would have floated in the runny frosting. I stuck with Betty Crocker after that.
I think I was 19 and I baked a turkey and my husband discovered I'd left the giblets in the neck.
My sister-in-law did that the first year she was married (I think she was 19 too), poor thing, her family never did let her hear the end of that.
Making custard in a crock pot. The screw up was with the recipe itself. It came out watery, well water pooled in some spots upon serving. Luckily I only made it for myself. Also when I was younger, I used to always wind up burning the green beans. I think because I tried to cook them too fast, would start doing something and forget I had them cooking.
Mashed potatoes last Thanksgiving. Josi talked me into trying them by a crockpot recipe she found. Bad idea. They ended up a lumpy mix of burned and raw.
I think that's the same recipe I tried once; do your mashed potatoes in the crockpot, they said; it'll be great, they said; they said wrong; it was a disaster for me too.