Egoism acts to impress is normal in life and but it's not good to over do it.

Normal
A scene with a teacher and a student and a group of student's friends

Teacher: You have to stay back after school on wednesday
Student: I can't, I've to go to bugis (expecting the teacher to question him/her)
Teacher: Why do you need to go to bugis?
Student: I've got some modelling to do
Teacher: Okay... (impressed)
Student's friends: Wa..


Over doing it
A scene with a friend(A) and another friend(B) with a group of friends in the basketball court

A: B, wanna join and shoot some hoops?
B: Nah... I've got leg cramps (expecting A to question him/her)
A: Why the leg cramp?
B: The other day.. went to gym, carried some 100kg weights, then.. muscle tear. nothing ah.... (with a pity face)
A: Oh okay...
The group of friends and A: LOL! (after B walked away)