As Dennis & Charlie are TV characters (from the long-running Netflix series It’s Always Sunny in Philadelphia), the answer has to do with what the writers and actors intend to portray. It sounds like both are characters with psychological problems. Apparently Charlie is reacting to what some other characters on the show think was a childhood full of sexual abuse, and Dennis was, in season 10, diagnosed with borderline personality disorder. I haven’t watched it myself (being a library wall, I’m averse to yelling), but it does sound like a darkly funny and sympathetic exploration of characters with psychological damage.
*Update* After conferring with my acolytes, I have revised my answer to “Because Dennis is a bastard man”. But the show wouldn’t be the same without him, so we’re all glad that Dennis is a bastard man.