Hi. How do you define the "pressing"? Was s/he literally right in front of you, begging you to try it? Or did s/he just leave it with you?

If it was the latter, you owe him/her no explanation for passing it on to someone else. Bless others with your excess. If there's no one to give it to, toss it. Bonnie hit the nail on the head here:

You now know that there's no such thing as one taste or one spoonful, so don't let others try to convince you otherwise. Maybe it's "just one day" or "just one meal" for them, but they aren't living in your body and mind.

If s/he was pushing you to eat it right then and there, you need to be tough. You don't necessarily need to be honest. I have no guilt fibbing to people if it's none of their business why I'm choosing not to eat a certain food. No one has the right to force you to eat something that you've chosen not to eat, just like they don't have the right to choose your clothing, your hair style or your home decor. The dessert was a gift. It was thoughtful. You're not obligated to genuinely love every gift you're given. You can thank the giver and move on.

Convenient excuses when someone wants to watch you eat the food that they lovingly prepared for you that could end up making you sick or dead:
- "I'll save it for later, thanks" with one of a myriad of excuses, if necessary: I had a big meal, I have heartburn, I feel under the weather, blah blah blah.
- "Doctor's orders - and I'm taking it seriously." Feel free in invoke any health problem they already know about.
- Add a "(spouse/child/etc) will be so excited to have this! Thank you!"

If it's escalating, add a "well, I've made a decision and it's not up for discussion. Let's talk about something else."

As for gatherings when friends/family offer you something off-plan, my favourite is a simple "No, thanks" and change the subject.

Bring something - maybe lots of things - that are on-plan. Jam-pack your plate with them. You'd be amazed at how little anyone cares about your latest diet and/or what foods you're avoiding if you just walk around with a plate full of chicken wings, LC jalapeno poppers, etc. Bring LC appetizers, LC pumpkin pie, a fabulous dip (dip veggies or pork rinds). Eat lots of turkey and vegetables. Complain loudly about how full you are.

If someone offers you something you'd rather avoid, remember that "No, thanks" is a complete sentence.

It can go deeper than that, I know. Your mom/aunts/grandma can take it personally when you decide that the food you were raised on is suddenly not good enough for you. It's like you're implying that you weren't raised right. Do your best to just change the subject, emphasize your health (tell white lies if you need to), and just plan ahead for nice ways to say it.

I was about to close this with, "good luck." But luck has nothing to do with it. I'll wish you strength instead. Stand up for yourself and for your health. No one else will.