This sounds like a good question for your manager. There's a reasonable chance you're not the only one who feels this way, and speaking up may help move the needle on Captain Cutoff interjecting their thoughts mid-someone-else's sentence.

What ever you do, don't lose your cool. You will not help yourself by saying "hey jackass, I was speaking, so shut your pie hole (mouth)." [1]

[1] Source: Used to lose my cool. It did not help. But therapy did :)