Barney is a womanizer, having slept with over 200 women.
Actresses, including the leads, frequently wear tops that expose a lot of cleavage.
Many scenes insinuate that some of the characters have just engaged in sex.
Many visits to strip clubs and mentions of casual sex.
Mentions of different sexual positions and people of whom the characters have "hooked up with" or "banged."
Friends with benefits is mentioned when two of the characters try it.
Many mentions of masturbation.
Also mentions of when the characters lost their virginity.
Some brief sex scenes where no nudity or actual sex is shown, but there may be brief sexual sounds made.
In one episode several men are seen naked. No genitalia is shown, but can be a bit lengthy.
There are many euphemisms used for sexual content.
Innumerable sexual references, including innuendos and sexual humor, some examples:
Season 1, episode 9: Shows three main characters at a strip club where we see scantily clad strippers with a lot of skin showing dancing sexually.
Season 2, episode 1: A couple is portrayed to be laying in bed naked, we can tell by the bare shoulders that our uncovered by the blanket. In another scene, a woman runs through the house in just a man's T-shirt. The same couple is shown naked together in the shower where we see both of them from the side. Her arms cover her breasts. In another scene, they go to a strip club, and women are shown wearing hardly anything, dancing on stage, with other characters, and walking around.
Season 2, episode 16: Shows female strippers on two different occasions which are shown dancing sexually in lingerie. A lot of sexual references and innuendos.
Season 2, episode 19: Entire episode revolves around a "battery-powered adult recreational fake penis."
Season 5, episode 2: Some main characters sit in a strip club, and women are shown scantily clad with a lot of skin showing, dancing sexually, and walking around. In another scene, a scantily clad UPS girl delivers a package, and he is made fun of for not fantasizing about other women besides his wife, so he tries.
Season 5, episode 6: A person makes a euphemism for "fuck" and says "bagpipes" instead when his neighbors make too much noise while having sex.
Season 6, episode 6: Main characters visit a strip club.
Season 7, episode 17: A couple is said to have made a sex tape. A woman starts making sexual movements and noises, trying to get another man to watch it.