Learn Hardcore Chinese: xiàbān yǐhòu wǒ gēn tóngshì shuō zàijiàn.

下班以后 – very common, neutral, and fine in almost all contexts.
下了班以后 – emphasizes the completion a bit more (literally “after having gotten off work”).

In everyday speech, people very often just say 下班以后 without 了, and it does not sound incomplete. In this sentence, leaving out 了 is perfectly natural.

What does 跟 mean here? Is it “with” or “to”? Why not 对同事说再见?

In 我跟同事说再见, 跟 can be understood as:

with: I say goodbye with my colleagues (we mutually say goodbye).
or “to”: I say goodbye to my colleagues.

In practice, 跟 + person + 说 is a very common pattern:

我跟他说明天的安排。
I explained tomorrow’s plan to him.

You could also say 对同事说再见, but:

跟同事说再见 sounds more like a mutual, social interaction.
对同事说再见 is grammatically fine, but slightly more about the direction of speaking (to someone) and feels less like a routine social exchange.

Everyday, natural choice here: 跟同事说再见.

Why is there no plural marker after 同事? How do I know it’s “colleagues” and not “colleague”?

Chinese usually does not mark plural on nouns the way English does. 同事 can mean:

one colleague
several colleagues
colleagues in general

You know from context. In this sentence, it naturally feels like “colleagues” because saying goodbye after work is usually to more than one person, but grammatically it could be either.

If you really want to make it clearly plural, you could say:

同事们 – colleagues (as a group; slightly emphasizes the group)
几个同事 – a few colleagues
很多同事 – many colleagues

Should there be a measure word like 个 before 同事?

Not in this sentence, because we’re not counting or specifying number.

You use a measure word when you have a numeral or something like that:

一个同事 – one colleague
三个同事 – three colleagues
那位同事 – that (polite) colleague

Here, 同事 is just a general object of the verb, so 我跟同事说再见 is correct without 个.

Can I omit the subject 我 and just say 下班以后跟同事说再见?

In context, native speakers could omit 我 if it’s very clear who is being talked about, for example in a longer conversation about your own routine.

However, as a standalone sentence, it’s more natural and clearer to keep the subject:

下班以后我跟同事说再见。

Chinese can drop subjects when they’re obvious from context, but learning-wise, it’s safer to include the subject until you’re very comfortable with when it’s okay to omit it.

Is 以后 always placed after the verb like in 下班以后, or can it come before?

With verb-related time expressions like this, 以后 almost always comes after the verb or verb phrase:

吃饭以后 – after (I) eat
下课以后 – after class is over
下班以后 – after getting off work

You would not normally say 以后下班 to mean “after work.” So the pattern is:

[Verb / event] + 以后

Would it be better to say 和同事说再见 instead of 跟同事说再见?

In this kind of sentence, 跟 is the natural choice.

和 and 跟 can both mean with, but:

跟 is more common with verbs like 说, 聊, 商量, etc.
和 is very common when just linking nouns:
- 我和同事 = my colleague(s) and I

So:

我跟同事说再见。 ✅ very natural
我和同事说再见。 – understandable, but sounds less idiomatic; most people would say 跟 here.

Why is it 说再见 and not just 再见 like in English where we just say “Goodbye”?

Chinese allows both patterns:

Verb + object:
- 跟同事说再见 – literally: say goodbye to colleagues
Direct quotation:
- 跟同事说：“再见！” – say “Goodbye!” to colleagues

In this sentence, 说再见 is treating 再见 as the thing you say (an object of 说). That’s very common and sounds natural.

In actual conversation, people often just say:

再见！
拜拜！ (bye-bye)

But when you describe the action in a full sentence, 说再见 is standard.

Does 再见 sound formal? When would you use something else like 拜拜?

再见 is neutral and appropriate for:

work
school
almost any polite context

It doesn’t sound stiff or overly formal; it’s just standard.
Alternatives:

拜拜 – casual, often among friends or in relaxed situations.
回头见 / 改天见 – “see you later / see you another day.”
明天见 – see you tomorrow.

In a sentence about normal work behavior, 跟同事说再见 is exactly what you’d expect.

Could I say 下班以后我跟同事们说再见? How does that change the meaning?

Yes, 下班以后我跟同事们说再见。 is correct.

同事 – can be singular or plural, neutral.
同事们 – clearly plural and emphasizes the group, like “my colleagues (as a group).”

Using 同事们 makes it sound a bit more like you’re addressing the whole group of colleagues. It’s a stylistic nuance, not a big grammatical change.