This will be my new line:

"Um...no thanks...Im a recovering binge eater and if I eat your sugary, carb loaded, crap filled food, I will lose control of my mind/body/soul again and eat until I throw up.  But really, thanks anyway!!!!!"

Oh, If only I could bring myself to say that to somebody...how do you think it would make them feel?!

Taking a deeeeep breath here....

You are entering the HARDEST part of this journey, maintenance.  You led yourself here with the diet.  And yes, you must still keep leading with the diet (and exercise of course), but now you are going to need to bring some new emotional/behavioral moves into this dance for it to work long-term in this dance-party of life. 

You are at the place in this journey where you need to realize that the way you eat will sometimes have some impact on other people in your life and they are going to need to make their own (MINOR, honest!) adjustments to this.  What happened to you yesterday was not an intentional assault aimed specifically at you, even though yes I know it FELT that way.  Honestly, it was an everyday happening of American life.  The eating plans changed.  In 99% of social situations, this would not be perceived as much of a problem at all.

In our American culture it is considered a "gift" to offer to feed something "nice" to someone else.  To momentarily take the "burden" of deciding what to feed ourselves off our weary shoulders.  As recovering binge eaters, we must quietly reject this tiny little piece of our culture and take 24/7/365 responsibility for every bite that goes into our mouths.  There's the rub.

Sure, you can go through this life exploding and judging and lashing out at people who "do this to you."  But honestly, over time, how do you think that's going to work for you?  If you alienate your husband's family, that's not apt to make him terribly supportive of these changes in you.

It doesn't have to be like that, I think it's a bad idea.  There are much better ways to handle these situations.  Quiet, calmer ways to eventually come out of this with your eating requirements taken care of and everybody's feelings okay about it.

Here's how I would have handled your situation yesterday.  When I heard we were going to have lasagna instead of eating out... "Oh that sounds lovely, but that's not going to work for me.  I don't eat lasagna.  We'll just stop off at fill-in-the-blank on the way home from church and pick up something for me to eat."
Then they'll probably get all flustered.  (See you don't even have to call them stupid idiots.  In fact, it's more effective if you calmly let them figure out for themselves that they did you no favor.) 

They'll likely say, OH!  blah blah blah... They might try to figure what in the meal you CAN eat.  (By the way, in my reply I always re-state it as I do and I don't, not I can and I can't.  That is a subtle way I indicate this is a fact, not something that is up for any kind of negotiation or that they can somehow give me permission for a break from that decision.)  Anyway, if you can eat, say, the salad, that's fine.  It might make THEM feel better.  Again, I think it's important not to lash out or judge their offerings, just calmly take care of your own needs and not make a big deal out of it.

Mostly, the less said, the less explained, the better.  Somehow without being rude or judgmental, you need to calmly emphasize that it's not their (or anyone else's) responsibility in any way to feed you, that you simply do not give that responsibility over to anyone else.  It is not their job (nor is it necessary) for them to UNDERSTAND anything about what or why you eat what you do, only that how you eat need have NO affect on what they eat. 

This rarely happens to me anymore, because I have learned (yeah, the hard way) that I don't go anywhere near a situation like this without having back-up food (in case of plan changes) with me.  I am quite possibly the only person on the planet who (discreetly) brought my own food to my son's wedding reception. 

The other fact about me is that I've been eating this way with the other people in my life now for more than 10 years.  They know/understand this about me, NOW they know it's nothing personal.  In short, we have ALL had time to make the required adjustments. 

It takes calm, not aggression.  It takes learning/practicing some new skills.  But it mostly takes time and patience, with yourself and others.