What do you do/think when this happens?

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Okay so when you're with your partner or anyone really, and he/she wants Mcdonalds or anything unhealthy ..what do you do?
I usually resist and sit there depressed watching him tease me with a burger.
Or sometimes having just one bite of something can satisfy me.
Occasionally I'll give in, and just eat along with it.

What do you do or tell yourself when you're in a situation like this?
What helps you resist or say no and eat something healthy?