"I will not harm her, by all saints I swear," Quoth Porphyro: "O may I ne'er find grace When my weak voice shall whisper its last prayer, If one of her soft ringlets I displace, Or look with ruffian passion in her face: Good Angela, believe me by these tears; Or I will, even in a moment's space, Awake with horrid shout, my foemen's ears, And beard them, though they be more fang'd than wolves and bears."
"Woah, woah, hey," says Porphyro, "I swear I'm not going to do anything creepy. In fact, I won't harm a hair ("ringlet") on her head; I just want to see her."
At this point, we still don't know what plan Porphyro's been cooking up, but we get some hints: he's promising Angela that he's not going to physically harm Madeline, and the way that he makes that promise (swearing he won't move so much as a hair on her head) makes it sound like he'd be in some position where he'd be standing over her prone body.
That… definitely seems to have potential for creepiness, right? What's more, Porphyro is promising not to look at Madeline "with ruffian passion," swearing up and down that he's going to keep things strictly G-rated when he sees Madeline.
This sounds like kind of a tall order for any young guy meeting his girlfriend in the middle of the night, but doubly so for Porphyro with his, you know, "fev'rous citadel."
He seems pretty serious, though, threatening to wake up all of Madeline's relatives, who definitely aren't pro-Porphyro.
Once again, the plume-and-tiara crowd from earlier are figured to be bloodthirsty animals. While you figure that this is just imagery, as you go through the poem it starts to feel more and more like these folks actually are animals.
They aren't goats, though, so don't be thrown by the "beard" comment. If you're wondering why Porphyro's threatening to put fake facial hair on his enemies, then wonder no more: "beard" here means challenge or confront.