Throughout the series, Dennis tries to bed as many women as possible to prove himself to others and sometimes to manipulate situations. His extreme vanity is one possible reason for this behavior, but regardless Dennis "bangs" more people on the show than anyone else. Dennis also keeps a camera running in his room at all times and a tape of all his encounters.
- In the first episode, Dennis was set up by Dee to have an unwanted sexual encounter with two gay men, which he does not remember due to being black out drunk.
- Dennis unsuccessfully attempted to pick up women at an abortion rally. ("Charlie Wants an Abortion")
- An attractive high school student comes on to Dennis in the bar, but he refuses her advances due to Charlie and Mac warning about her age. Once they learn she is 18 they give him the go ahead, but she has gone back to her old boyfriend. ("Underage Drinking: A National Concern")
- In the episode "Charlie Has Cancer", Dennis sleeps with The Waitress.
- Dennis and Mac hold a competition on who can bang Rebecca Keane first. Dennis wins the competition and rubs it in Mac's face ruthlessly. ("The Gang Finds a Dead Guy")
- Dennis attempts to seduce both Mac's mom and Charlie's mom in the same episode but is refused. He breaks down and cries after these rejections. ("Mac Bangs Dennis' Mom")
- Dennis picks up a girl at a fundraiser while acting like a humanitarian with Bruce Mathis. ("Dennis and Dee Get a New Dad")
- In the season premiere, Dennis drops acid and bangs a hippie named Asriel in an elaborate plan to ruin the life of her boyfriend, Sage.
- He seduces Margaret McPoyle in Paddy's bathroom in an attempt to escape from execution. ("The Gang Gets Held Hostage")
- In "The Gang Sells Out" Dennis sets a record for getting phone numbers from what Dee calls "bar-whores".
- In "The Gang Gets Whacked" two-part episode Frank pimps out Dennis to old and ugly women. There are several encounters in this episode most notably being the mob boss' wife. ("The Gang Gets Whacked (Part 1)"), ("The Gang Gets Whacked (Part 2)")
- As his role of "The Looks" in the gangs paradigm, Dennis tries to bang a female banker. ("The Gang Solves the Gas Crisis")
- Dennis has a fixation with anonymous sex as shown in the "Mac and Charlie Die" two-part episode: after trying an orgy with Frank, he finds a European roommate. ("Mac and Charlie Die (Part 1)"), ("Mac and Charlie Die (Part 2)")
- Dennis' erotic life is chronicled in a book of memoirs, some of which are true. ("Dennis Reynolds: An Erotic Life")
- For a brief time Dennis was married to his school sweetheart, Maureen Ponderosa. ("Mac Fights Gay Marriage"), ("Dennis Gets Divorced")
- Dennis gets refused by Jackie Denardo, a large-breasted TV reporter. ("The Storm of the Century")
- After a small road accident, he meets Elena and later receives a handjob from her. ("Thunder Gun Express")
- Dennis was forced to bang his ex-wife, Maureen Ponderosa, by her new fake large boobs. ("The Maureen Ponderosa Wedding Massacre")
The Paddy's Pub Blog released several lost chapters from Dennis' Memoirs:
- "Memoirs with a Geisha" - Dennis meets an older Japanese woman 
- "Like a Virgin" - Dennis bangs a drunk girl (which looks a lot like Dee) 
- "Knight Ride Her" - Recounts a story at a Medieval Times restaurant 
- "Cirque du So Laid" - In this story, Dennis bangs several members of a circus 
The first two chapters of the memoir were made into a bonus featurette for The Complete Season 4 DVD.