Most bad meals are some combination of bad ingredients and careless cooking.

Without having been there to witness, my guess is that the sauce was watery, with a slightly acid taste, made from store brand tomatoes and/or tomato sauce, tossed into a pan and heated up, rather than actually cooked. Any spices added had probably been sitting in the cupboard for years past the time they'd lost their flavor. The veggies probably were frozen, and freezer burned--from a horrid bag of mixed vegetables with cubed carrots, cut up beans, wrinkled peas, and random kernels of corn.

The easiest secret to good cooking is to use fresh ingredients and to prepare them simply. Beyond that, it is important to know what you need to do to get whatever you are cooking to taste good. It also helps to be able to follow directions. All this is cold comfort, however, because the truly bad cook is impervious to suggestion.

Without getting into personal details, we have had many meals like this to contend with--my sister, who lives close to home, simple eats before going over. I live far away, stay in a nearby hotel when visiting, and simply invite them for dinner at the hotel--on one ocassion, a major holidays, I cooked a meal for 15 in our hotel room and took it over, much to the appreciation of the guests.