What is the difference between 〜してんじゃねえ and するんじゃねえ?

Question

「糧食、エナジーパック、弾薬、修理部品は所定数を確保済み。ああ、どっかの馬鹿戦隊長のために、足回りの修理部品は多目に用意しといたぜ。おめぇ、簡単な修理は出来るんだよな」

「ええ。よく壊すので」

「しれっと返してんじゃねえよこのクソガキ。……持ってけるのは一機だけだ。同じ調子で戦うんじゃねえぞ」

86─エイティシックス─ 安里アサト

I notice that both 〜してんじゃねえ and ～するんじゃねえ can mean "Don’t do…". So is there any difference between the two expressions?

Answer 1

～してんじゃねえ is short for ～しているんじゃねえ (see this), so する is in the progressive/perfective (-teiru) form. Thus this only refers to what's already going on or what just happened.

On the other hand, ～するんじゃねえ does not have the progressive -teiru. It can refer to both what's going on now and what's going to happen in the future.

• 泣いてんじゃねえ。
  Hey, don't cry. / Stop crying.
  ^{(said to someone crying now)}
• 泣くんじゃねえ。
  Hey, don't cry.
  ^{(said either to someone crying now or to someone who may cry in the future)}

In the context in question, しれっと返してんじゃねえ and しれっと返すんじゃねえ are interchangeable. 戦うんじゃねえ is not interchangeable with 戦ってんじゃねえ because the battle is not in progress now.

Answer 2

@naruto said it excellently. I might put it more simply as the difference between:

1. telling someone not to do something either right now or in the near future
   = するんじゃねえ。
2. similar, but referring to whatever has just now occurred / is going on now
   = してんじゃねえぞ。

Also, to state the obvious, never ever use this expression in real life unless you want to sound very hostile beyond blunt.

You should also learn, while you're at it, to use "じゃないよ" instead of "じゃねえよ", in case you want to sound blunt and slightly careless just like from the book.

Example:

• 「いいね、待ち合わせにはくれぐれも遅れるんじゃないよ。」(future)
• 「泣くんじゃないよ。まだここからが勝負なんだ。」(present)
• 「なに、万引きしてきただって？馬鹿やってんじゃないよ!」(recent past)

In such cases, it covers "current events" "future events." It also allows the speaker to handle "recent past events" by making remarks on them right now, using the expression.