There's one quest in which you slut-slam a promiscuous lady in Riften - Haelga, as mentioned before. If you peek into her bedroom, there's some pretty suggestive stuff in there though.
In Sanguine's daedric quest (which you begin by accepting a drinking contest in a tavern), in your drunken haze, you're accused of "fondling the statuary" in a Dibellan temple by a priestess. The "consummate our love" line also comes from this quest.
You also get a "Lover's Comfort" bonus if you sleep with your spouse, though I'm not sure if that would count, seeing as how you have to be married to get this.
EDIT: Oh and I nearly forgot, in Dragonbridge there's a young lady whom an Imperial soldier tried to assault. There's nothing else said about that later though.
There's also gay marriage in the game, if that's the sort of thing your dad's against. However, it only seems to apply to the player character, as you'd be extremely hard-pressed to find another gay couple anywhere else in the game.
But really, the most suggestive content comes from the books in this game, rather than the quests.
'The Real Barenziah' book series is basically a recounting of the main character's many affairs over the course of her long life and how they effected Tamriel. It even includes an abortion.
'Thief of Virtue' is a saucy romance novel.
And then there's also the ever-popular 'Lusty Argonian' series.
Aside from that, Skyrim's a pretty clean game. The previous games contained a lot more sexual content. For instance, in Morrowind there's a dremora who threatens to rape you, a sleazy guy who invites you to his house (it's not possible to say yes to him) and a man who's involved in the Main Quest who demands that you a strip tease for him and give him a kiss before you can progress. There's an outrightly-professed necrophiliac in Oblivion. Ah, and in Daggerfall and there is no such thing as underwear.
In conclusion, I believe that Skyrim is the game that is catering to a wider audience and thus, does not include much sexual content at all.
