There's no sex on stage in Henry IV Part 1, at all. Come to think of it, Hotspur's wife makes a very big deal out of the fact that she's neglected by her husband, who's too busy fantasizing about getting his battle on.
Still, every Shakespeare play has at least a handful of characters with their minds in the gutter. And, since most of Shakespeare's characters are card carrying members of the WTTF (World Trash Talk Federation), there's lots and lots of dirty talk in the play, especially in the tavern scenes. (We dare you to count the number of bawdy jokes in Act 2, Scene 4.) Even Lady Percy, who doesn't frequent taverns, likes a little double entendre action now and again. She's always threatening to break her husband's "little finger" or his "head" (like when he cracks a joke about hooking up with another man's wife). Still, by Shakespeare's standards this stuff is pretty tame and more PG-13 frisky than anything else.
So, why are we giving the play an "R" rating? Well, Hotspur has a tendency to use graphic rape imagery when he talks about his penchant for combat. We talk about the overall implications of this in "Warfare."