Somebody wrote this to me;

おっさんはやく仕事しろっ て

right before exiting a chatroom. I feel like I've seen this sentence before.

Is it an expression? What does it mean?

Probably, 'The old man says hurry up and work.'
おっさん　（は）　はやく　仕事　しろ　って　（言っている）

.

Thanks so much to both of you! *muah muah muah*

Arupan Wrote:While I agree with the above comment, in this case it would most likely be が instead of は.

And theoretically there's another possibility - that he said おっさん to someone else in the room and he already told him that he should work before that.

It was a private chatroom with only him and me.
Also, could おっさん refer to a boss or is it literally "old man"?

It's not entirely literally 'old man' anyway. It's literally 'a man around middle age'; however, we have no good expression for that in English. (And we do use 'old man' less than literally as such a reference sometimes.)
It's probably a reference to a boss or an older relative. I don't know the guy's circumstances or what the 仕事 is so I can't really say.

This could also be him calling *you* an おっさん and telling you to get to work. The internet is full of people who like to insult strangers- even in Japanese. But without context we'll never know ♪

When I first read it my immediate interpretation was "Get to work, you old man" -- the って can mean someone else is saying it but sometimes people put it after what they're saying as well to mean something like "I'm telling you". It could be someone telling him to work too, though.

SomeCallMeChris Wrote:It's probably a reference to a boss or an older relative. I don't know the guy's circumstances or what the 仕事 is so I can't really say.

This seems most likely.

Both おっさん and ばば can be derogative references to your parents.
仕事しろ can be a generic stop loafing or stop being lazy expression.

Thus if the speaker was young and living at home then something like, "My dad told me to hurry up and get back to work." == "My dad told me to stop frakking around on the internet."