One place we see Sammy concerned with how people perceive him is in his pronouncement of quitting his job at the grocery store:
The girls, and who'd blame them, are in a hurry to get out, so I say "I quit" to Lengel quick enough for them to hear, hoping they'll stop and watch me, their unsuspected hero.
It's not just a matter of principle at stake here. If Sammy truly quit as an act of empathy for the girls' embarrassment, he could have quit at the end of his shift or even in a private moment with his boss. Instead, he is sure to voice his departure loudly and notes that he hopes the girls hear him. Sammy wants to be seen as their hero, which ends up being a futile effort on his part.
Sammy's boss is actually friends with his parents, so he tries to get Sammy to reconsider making such an impulsive decision on behalf of these girls he doesn't even know. Here we again see Sammy's concern for perception:
But it seems to me that once you begin a gesture it's fatal not to go through with it.
Sammy feels that he can't back out now because it would make him look weak or noncommittal to everyone watching. So he holds his ground even though he silently agrees with his boss that he will feel this moment for the rest of his life.
As he goes outside, Sammy is hoping that his heroic gestures were enough to make the girls wait for him in the parking lot. He notes, "I look around for my girls..." as he exits the store. Again, his motive doesn't seem to be that of genuine concern for their embarrassment. His goal was to be noticed by the girls for acting on their behalf. Even as he looks for them, he realizes that they have gone, noted by the "of course" in his reflections.
He tries to play the part of a hero, but Sammy falls far short in the eyes of the girls and of himself in the end. And maybe that's why he realizes the world is going to be tougher than he'd anticipated.