Quote 25
The erection made me feel guilty in hindsight though, but I guess it couldn't be helped. (3.5.26)
Charlie is having a completely normal physiological reaction to getting a compliment from someone who is attracted to him. But his past experience turns something that should be a little pleasurable into a source of guilt.
Quote 26
Each [cover] had a smiling face, and every time it was a woman on the cover, she was showing her cleavage. (3.8.3)
Even in the '90s, sex was everywhere. It's not just Charlie's family and friends who expose him to sexuality—just walking past a newsstand can do it, too.
Quote 27
It was like everything made sense. Until she moved her hand under my pants, and she touched me. [...] It felt good actually. [But] I didn't know what was wrong. (4.14.51-54)
This should be a wonderful, pleasurable moment for Charlie, something that he's been secretly wanting since the moment he met Sam. But because of his history, it causes a lot of repressed memories to come gushing to the surface.