From my experience, if you keep declining yourself stuff like that, you are setting up yourself to fail. Have that pizza, just remember to not go and stuff yourself to the point where you can’t walk because you’re full. Remember to eat slowly too.
you can also just make small modifications to decrease the calorie density of your meals, adding veggies is great.
Also, life hack: you can eat basically as much fruit as you want when dieting, it's so filling (due to the water and fibre) that you're almost guaranteed to be full and probably quite sick of it before you consume a ton of calories.
See, I'm an all or nothing kind of person. "Just the one slice" doesn't work. I eat the whole pizza. I've had much more success with regimented diets. The one I've settled on, which has worked well for years, is intermittent fasting. I only eat in a six hour window and this basically means two satisfying meals of whatever. I have to try hard to overeat in that window. It also helps to cut down on snacks.
Everything in moderation. Have pizza, but limit yourself to 2 slices, have a big delicious salad with it (no creamy dressing). Small treats like this is what makes a diet sustainable.
Healthy habits stack, and maintaining a streak can be a great way to keep good habits going. If that's what keeps you going, keep doing it!
However, don't deprive yourself so much that when you do slip up you say "Fuck it" and go on a binge and eat a Taco Bell 12-Pack.
Give yourself permission to eat food you enjoy in moderation, and have a plan in place to prevent a full fall-off-the-wagon moment when you do eat some pizza and tacos.