just 後用did還是done?

正確用法係 have just +pp
所以要用 done,但一定要有have or I've系前面!
而家好多人都用錯咗

I just done a very stupid thing.

Can be both, but depends on whether you are going to use (has/have) before the verb.

I just did a very stupid thing/ He just did a very stupid thing.

or

I have just done a very stupid thing/ He has just done a very stupid thing.


For other examples:

She just went to work or She has just gone to work.

What I just did was super stupid/ What I have just done was super stupid.

He just knew the bad news/ He has just known the bad news.

When to use past tense:
When time is mentioned, such as yesterday, last year, an hour ago, in 1997, etc., past tense must be used.

When to use present perfect tense:
When the event has been completed and the time of the event is not mentioned. "Since" does not tell the time of the event but only from that time onward.

"I just did a stupid thing" is correct, meaning I did the stupid thing just one moment ago.

"I have just done a stupid thing" is also correct, putting the emphasis on the fact that the event has happened. The sentence can mean that the event took place hours or days ago.

just did

When you see 'just', usually we use present perfect tense.
i.e. I have just done a very stupid thing.

It's wrong to write I just 'done' a very stupid thing.
It's because a complete present perfect tense has to include has/have + past participle.
i.e. has/have done but never write done without has/have

I just did a very stupid thing.

睇情況la...............