In this section of the soliloquy, Hamlet is questioning both his bravery and resolve. Those lines read:

Who calls me villain? breaks my pate across?
Plucks off my beard, and blows it in my face?
Tweaks me by the nose? gives me the lie i' the throat,
As deep as to the lungs? who does me this?
Ha!
'Swounds, I should take it: for it cannot be
But I am pigeon-liver'd and lack gall
To make oppression bitter, or ere this
I should have fatted all the region kites
With this slave's offal: bloody, bawdy villain!
Remorseless, treacherous, lecherous, kindless villain!
O, vengeance!
Why, what an ass am I! This is most brave,
That I, the son of a dear father murder'd,
Prompted to my revenge by heaven and hell,
Must, like a whore, unpack my heart with words,
And fall a-cursing, like a very drab,
A scullion!
Fie upon't! foh! About, my brain!

The line "Who..plucks off my beard"? is Hamlet's wondering who has let him feel like he is less than a man. A bearded man was an adult versus a child who is not mature. In Hamlet's thinking, he himself has allowed Claudius to emasculate him.

Why, he chastises himself, is he allowing the villainous Claudius to get away with murder and treachery? Hamlet knows he has done little except talk and fume uselessly "unpack(ing) his heart with words". The time has come for action. By the end of the soliloquy, he has strengthened his resolve and come up with the plan of entrapment that he hopes will fell Claudius and his complicit mother.