To describe the context...Girl A and a boy arrange to go to an amusement park to find some clues about...something. Or that's what she says to him, but the girl is actually tricking the boy into going on a date with her. With this in mind, the boy then goes to girl B and asks her to come to the amusement park as well, thinking that she might help. He doesn't explain the situation, so girl B thinks that he is asking her out on a date. They all meet at the amusement park and the girls get upset because there are 3 people when there should only be 2 and they don't want to talk anymore. The boy goes to buy some juice.
So now, girl B complains to the other girl: あいつはクズよ！！今日だってもう少し説明しろってのよ！！ At the same time, the boy, now alone, talks to himself: 早く家に帰ってゲームしたいのに・・・さっさと話し合いしろってんだ。
To me it feels like the sentences would translate as "He is garbage!! Today too, I mean, explain a little more, damn it!!" and "Even though I want to get back home sooner and play games...I mean, get talking already." So then, is the subject of ってんだ the speaker?
Someone told me that it's actually similar to というのは but I don't understand how it is possible when the imperative is used.