When you are proud of something and someone tries to take you down by condescending or acting nonplussed, try to eliminate this person and his likes from your life or at least spend as little time as possible with them.
Before you try making radical changes, accept the state you are in; you may harm yourself if you try to change without acknowledging your inherent value first. Consider yourself a flourishing garden that needs pruning, watering and general upkeep.
To do better in school, you need to tell yourself some encouraging words like “I am hard working and intelligent, I have ambitions and dreams and I am capable of achieving them”, instead of saying “I am too lazy and stupid”. You can work on your plan of action once you have a positive framework.
Reframe your perspective of self- improvement; tell yourself “I need to learn how to listen better” rather than “I need to stop talking too much”, and instead of “I am fat and I need to lose weight”, try “I will work on taking more care about my body by eating better and exercising more”.
Keep in mind that being less than a supermodel is not a flaw; you are just fine and normal. A very tiny percentage of people can come close to looking like an actor or a model; most people are not born thin and gorgeous, not to mention that those people have a whole team of personal trainers, designers and make- up artists to produce this image.
Of course you will be unhappy if you hold yourself up to an unrealistic standard. Unfortunately, school does not grade your artistic abilities, your ability to work hard or how athletic you are, so it is not necessarily a flaw that you are not a great student.