I've eaten really bad today...

Regarding weight loss, you probably won't even go over your calories for the day, you're fine. Don't stress about it.

But yeah if you're allergic, you shouldn't be eating that then...

One bad day of eating won't ruin your progress. Trust me, I've had my share of bad days! You may see an increase on the scale in the next few days thanks to water retention due to the excess sodium and carbs in the pizza. If that's going to throw you off then don't weigh yourself for a few days!

The next thing to do is assess the damage. Log the pizza, even though you don't want to, and see how bad it is. Can you make it work, anyway?

Personally, I would recommend eating a sensible dinner no matter what the calories in the pizza looked like and workout a little harder to make room for it. But I try not to punish myself for a bad day because I don't want to get into a food-is-the-enemy mindset. You'll have to decide what works for you.

Learn from this and decide how you want to deal with it next time. There will always be unexpected pizza and donuts and whatnots in life. Do you want to say no to them forever or be able to partake in a sensible portion? That's where the whole lifestyle change instead of diet advice really comes into play.

A little slip is ok just don't make it in to a daily occurrence. You didn't gain the weight in one meal and you wont loose it in one. Treat yourself every now and then, people say it will help your body by convincing it that there is going to be more calories and it doesn't need to hold on to every last calorie.

Maybe use the calories to do a little more exercise.

Say 10 Hail Mary's, eat a 4.8 ounce chicken breast and some steamed cauliflower as penitence.

Pizza is not the enemy. It won't kill you.

Except Pizza Hut. That stuff is the devil.

I will never understand what is wrong with pizza.

That said, your teacher bought you pizza? Are you old enough for this site?

Don't beat yourself up! I had a box lunch at work today due to a long meeting, and I ate the bag of potato chips that came with it, despite initially setting it aside. Something about being in a meeting for 4 hours gave me a salt and fat craving.

Just log the calories, take a look at your daily total, and go from there. In your shoes, I would still eat a reasonable dinner--maybe a little lighter than normal--and try to make up any calorie excess over the next few days, rather than all at once. I logged my potato chips, and I'll take the equivalent calories out of dinner.

Remember, you're in this for the long haul, and if you're good most days, you can allow yourself indulgences from time to time. No one is perfect, and you need to eat now like you'll want to eat the rest of your life.

I just ate a big tub of yogurtland tart so you're not alone. but log it, see the damage and hit extra gym time if you must. eat smarter for dinner and drink lots of water to help your body feel not so polluted. that's my plan.

You can't beat yourself up for one day of slipping up. We all have those days and they won't hurt your weight loss progress (It's just one day, after all). Just tell yourself you won't do that again for a while. This can be your "fatty-food day" for the month.