Souma is really susceptible to cracking up, and even memories will put him into laughing fits. But being self-conscious about this, he always tries to hide it. When he does this again at a clothing store his friend works at, the friend asks him why he does that, especially when it's so easy to tell anyway. Later, Shun also repeats the same sentiment...
I'm actually quite conscious 
of how people perceive me.
أنا مُدرك لنظرة النّاس لي حقّاً
Und ich ertrag die Blicke
der anderen Leute nicht …
No me gusta que la gente me mire.
No me gusta que la gente me mire.
Le regard des gens me dérange.
Io faccio molta attenzione
agli sguardi degli altri.
Eu me preocupo com a forma
que as pessoas me enxergam.
Я знаю, как выгляжу со стороны.