
Bruh, he has severe PTSD and it's basically engraved into his brain that he shouldn't have negative reactions to being sexually assaulted or raped, of course deep down he was hurting and disgusted but he felt like he couldn't open up about it, he had lived his entire life being treated like that so of course he doesn't know how to react properly to it.

did you read the rest of the story? the rest of the story confronts why he always smiles when bad stuff happens to him. the reason why he is able to act nonchalant and why. There’s The whole scene where he cries for the first time in years and admits to hating everything that’s happened to him. It’s a story about a broken person who smiles when horrible shit happens to him because his mom pawned his body off since before he reached double digits.
This wasn’t the first time he was raped either, it happened to him multiple times. That’s why he’s able to act like this. There was also the thing where he was like “oh you think I’m dirty now” where you could see his façade breaking.

You clearly have no idea how ptsd works do you, someone's common sense is easily altered after trauma, especially if that's what they were taught from a young age. doesn't have anything to do with him being dumb or not, and he doesn't "need his ass beat" for being a victim of trauma, it doesn't matter if we're talking about a manga or not but coming from a person with ptsd, what you're saying is fucking disgusting and uneducated, so before you spout shit please do some research or be quiet.

here is why he did not like being raped & that his reaction makes sense:
him explaining how his mother played a part in his emotional trauma & what caused his trauma:
http://www.mangago.zone/read-manga/yatamomo/mf/dec5c732ec4804308b5b616bb3c3c71b_chapter-4/pg-7/
http://www.mangago.zone/read-manga/yatamomo/mf/dec5c732ec4804308b5b616bb3c3c71b_chapter-4/pg-8/
him OUTRIGHT SAYING that he hated the sexual actions he had done in the past AND saying it was his only way to live:
http://www.mangago.zone/read-manga/yatamomo/mf/dec5c732ec4804308b5b616bb3c3c71b_chapter-4/pg-15/
AND MOST IMPORTANTLY
this is the part where he says “laughing when it was convinient has left me anesthetized”
(anesthetic: insensitivity to pain)
http://www.mangago.zone/read-manga/yatamomo/mf/dec5c732ec4804308b5b616bb3c3c71b_chapter-4/pg-14/
according to mayoclinic.org “Refusing to acknowledge that something is wrong is a way of coping with emotional conflict, stress, painful thoughts, threatening information and anxiety. You can be in denial about anything that makes you feel vulnerable or threatens your sense of control...You can be in denial about something happening to you or to someone else.
When you're in denial, you:
-Won't acknowledge a difficult situation
-Try not to face the facts of a problem
-Downplay possible consequences of the issue”
(article: https://www.mayoclinic.org/healthy-lifestyle/adult-health/in-depth/denial/art-20047926)
So Momo is saying that instead of dealing with pain, he laughs it off and “downplays the possible consequences of the issue”. Momo is traumatized, and by your definition, a slut who sleeps around with people. But he is still a person and he obviously didn’t enjoy the rape, his brain was conditioned to react that way and laugh it off because he didn’t want to “bother other people with his issues”.
this is the instance where you can see symptoms of his trauma come through when he thinks that he is going to be “thrown away” for no reason and comes up with reasons that make no sense but he justifies it to himself because that was the way he was treated in the past (ex. Suda)
http://www.mangago.zone/read-manga/yatamomo/mf/manga/yatamomo/c005/pg-15/
http://www.mangago.zone/read-manga/yatamomo/mf/manga/yatamomo/c005/pg-16/
http://www.mangago.zone/read-manga/yatamomo/mf/manga/yatamomo/c005/pg-19/
http://www.mangago.zone/read-manga/yatamomo/mf/manga/yatamomo/c005/pg-13/
http://www.mangago.zone/read-manga/yatamomo/mf/manga/yatamomo/c005/pg-13/
Please let me know if there is anything you are confused about or if you need further clarification, because although i tried to make it organized as possible with as many resources and evidence as possible, it is a lot. I also just want to let you know I’m not trying to attack you, I just want to get my own point and perspective across.
Holding hands with the seme and talking about relying on him right after getting fucked by another guy and freely telling it to him and not even feeling a little bit of guilt or remorse. Hmmmm