particle が - What is the meaning of the 「が」 in 「仲間だろう が！！！！」

It is from a line in One Piece:

Another instance from the same manga:

Answer

According to this article, 三省堂国語辞典 says:

「だろうが」「でしょうが」などの形で文末につき、「念をおして相手をなっとくさせようとする気持ちをあらわす」（『三省堂国語辞典』）

And デジタル大辞泉's entry says:

[３]［終助］
２ （多く体言や体言の下にののしる意の接尾語「め」を伴ったものに付いて）ののしりの感情を強める。「このあほうめ―」「あいつめ―」「敵(かたき)の回し者め―」〈伎・幼稚子敵討〉

I think those pictures show its usage better than a hundred words. This が was used because they were upset, and they tried to strongly convince people in front of them.

• 言ったでしょう？　I told you, didn't I? (already accusatory)



• 言ったでしょうが！ (even stronger)