The Perks of Being a Wallflower lends itself to analysis because of the many uses of different literary devices and techniques. However, some of your considerations are going to be more than single events; instead, they will stretch over the entire course of the text. For example:

Theme

One of the central themes of the book is that participation is key to getting the full experience in life. Charlie is a “wallflower.” His primary mode of being is as an observer instead of a participant. Being an observer rather than a protagonist gets him into trouble, like in his relationship with Mary Elizabeth, whom he mostly dates because he cannot work up the courage to tell her he doesn’t want to be in a relationship. He eventually makes the drastic move to kiss Sam instead of her at a party during a game, and she remarks later that she is okay because he never talked enough. However, the break-up does negatively affect Charlie, who is essentially abandoned by his friends. One of the most significant parts of the story is that Charlie comes out of his shell by the end. Sam and Patrick work diligently to show him how to live his life to the fullest, and he learns by the end that participation is key to experiencing what life has to offer.

Irony

One of the most ironic moments in the text is when Brad mistreats Patrick for being gay, even though they are having sex. It's ironic because Brad is a closeted gay man, and yet he abuses Patrick because he is openly gay. It is also ironic that Patrick still has sex with Brad despite the way Brad treats him.

Dynamic Character

Charlie is the epitome of dynamic, because he changes in nearly every letter of the book. Sometimes the change is simple, like learning something new or being exposed to a new activity, and sometimes the difference is profound, like when he learns that he was sexually abused and decides to participate more in his sophomore year at the end of the book. Charlie is one of the few characters that changes so much in the book. Many of the other characters, with the exception of Patrick, stay roughly static in their personalities and interests—likely because we see them from Charlie’s perspective as a younger person looking up to older friends.

Inciting Incident

This is an interesting device because it is not typically included in the list of literary terms, but an inciting incident sounds like an incident in the text that builds conflict that must be overcome. One such incident is Brad beating up Patrick after his dad catches them together. This creates conflict because Charlie has to rescue Patrick. Subsequently, Charlie is brought back into the friend group and has to deal with his feelings for Sam. Charlie coping with his feelings for Sam is one of the central issues in the text, and it makes sense then that the conflict between Brad and Patrick might bring that back to light, given Charlie’s loyalty to Patrick.

Climax

The climax of the story is when Sam and Charlie are nearly able to be together. They are finally together, the conflict between Charlie and his feelings is resolved, but in the falling action, we see the blowback from their passionate embrace. Charlie falls into a catatonic state and has to go to a psychiatric hospital. He eventually comes to terms with abuse from his past, but we see the resolution that Sam and Charlie are still close after their time together during the climax of the story.

Stephen Chbosky’s The Perks of Being a Wallflower, is about emotional devastation and interpersonal conflict:  Charlie’s best friend, Michael, has committed suicide; Patrick experiences public humiliation and repeated sorrow emanating from his sexual orientation; Charlie, it is finally revealed, was sexually abused by his beloved aunt; Charlie’s sister has been physically abused by her boyfriend.  In discussing Michael’s suicide with his dead friend’s former girlfriend, Susan, Charlie experiences an epiphany of sorts:

“It suddenly dawned on me that if Michael were still around, Susan probably wouldn't be ‘going out’ with him anymore. Not because she's a bad person or shallow or mean. But because things change. And friends leave. And life doesn't stop for anybody.”

The theme of the novel lies in that quote:  Life is about overcoming challenges.

The irony involves first and foremost the role the deceased Aunt Helen played in Charlie’s life.  Early in the story, Charlie writes:

“My Aunt Helen was my favorite person in the whole world.”

 Throughout the story, Charlie lovingly references Aunt Helen and how close he and she were before she died.  Subsequent revelations regarding Helen’s dark secret (“I will just say that my aunt Helen was molested. I hate that word. It was done by someone who was very close to her”) and her subsequent abuse of Charlie, strongly hinted at in the following quote, lead to the realization that Charlie’s emotional problems may be tied to the sexual abuse he experienced at the hands of the person he trusted most:

“When I fell asleep, I had this dream. My brother and my sister and I were watching television with my Aunt Helen. Everything was in slow motion. The sound was thick. And she was doing what Sam was doing. That's when I woke up. And I didn't know what the hell was going on”

Charlie is a “dynamic character,”  who undergoes emotional and intellectual transformations.  At first, he is a shy, awkward, emotionally troubled freshman, tormented by Michael’s suicide and the death of Aunt Helen when Charlie was seven.  By the end, he has developed interpersonal skills, experiment with drugs and sex, and accepted that life has to be lived to the fullest even through emotional pain.  In the epilogue, he comes to terms with the fact that everyone has problems and that growing up means learning to handle them:

“ . . . we could all sit around and wonder and feel bad about each other and blame a lot of people for what they did or didn't do or what they didn't know. I don't know. I guess there could always be someone to blame.”

An inciting incident in the book could have occurred before the story begins: Michael’s suicide, which provides much of the deep-seated anguish experienced by Charlie.  Similarly, Aunt Helen’s death when Charlie was seven could be considered the book’s primary inciting incident.  Within the pages of the book, however, Charlie’s surprise observation of Patrick and school athlete Brad kissing could also qualify as the incident that propels action forward.  The story’s climax, Charlie’s realization that he was sexually molested on a regular basis by his beloved aunt, has been discussed in the context of irony.