That sounds pretty mean. I don't think your mom would be anywhere close to being happy if you tell her that. There are few things and the way you say it can hurt your mom's feelings.
1. You don't just tell her "Mom, your cooking sucks." or "Mom, I think you should get a cook book."
2. You don't go out there and just grab a burger.
3. It's mean of you to say that you hated it all your life, although deep down you yourself know it does.
4. If you loose your mother someday, you will realize how wrong you were and how you wished you could take your words back about this.
5. She cooks because she cares about you. If she didn't, she wouldn't even bother to even cook. She's doing her best.
Here's a thought about your problem: I think it's your mom's problem that maybe she didn't learn how to cook. How about talking to her privately and tell her NICELY and make sure YOU MEAN IT BECAUSE YOU CARE "Mom, please dont get me wrong, I hope you won't get mad at me if I tell you this. And please don't get upset. I really love you, but I don't think I love your food."
First: I think she would laugh at thay. Second: That's a smooth way of telling her. Third: You're going on through this by yourself and make sure that you're telling her really nicely that it won't hurt her feelings.
However: If she's sensitive and the next day she starts acting weird the next day, tell her "Mom, I'm just telling you the best I can and I want to be honest with you. Why do you need to act weird all of the sudden?"
If she's been really weird to you and sounding mad with you and mean with you, tell her "I gain pounds all because of eating McDonald's everyday, Mom." and run up to your room and lock the door.
I hope it'll work. Wish you luck. Remember, don't be mean to her.