to talk incessantly, and at length, AT another person, trapping them in the situation and not allowing them time to reply.
a person sermonising to another, perhaps when drunk, who cannot be steered towards to a different topic, is said to have he audience in a verbal headlock.
"she was really mad, had me in a verbal headlock for an hour."
"my ears are bleeding! he didnt shut up, i was in a verbal headlock"