Good At vs Good in

I don't think its correct to say good in,or is it?

I hear some women say: He is good in bed.

If this is correct, I would like to know the rules when to use good at and good in, if you please. Thank you very much.

daddyjohn know you say Good at English. (correct)

When do we use Good In?

He is good in bed is different. Does it make sense to say 'He is good at bed'?

Thank you for your reply.

so are there any rules regarding the use of good at and good in?

'Good at' indicates ability, whereas 'good in' doesn't.

Similarly, poor at and poor in.

He is poor at English. (lacking in ability)

The soil in poor in nutrients. (lacking in quality)

I hope this helps.

That's very useful. Many, many thanks again!

You're welcome.

I know this was posted a few years ago.. but..
I was also looking for the rules..
I just remember at one of my English Grammar Seminars we discussed that either of good at or good in is used for skills and the other one is used for subjects/topics..
good at + subject/topics
She's good at Math.
She's good at Swimming.
He's good at parenthood.

good in + skills
Sh