I am writting to ask about the connotation of the idiom speak of the devil?

Is it humourous, disapproving, or neutral?

If I see my friend who I have just been talking about. I assume if I use this idiom for him, he might get offended if I don't express it in humourous way.

Am I right?

In addition, what is the opposite of this idiom? I mean can we say speak of the angel in contrast to speak of the devil ?

Do we have similar idiom conveying that meaning?

I take it as a neutral statement.

There isn't really an opposite, but the person being spoken about could say "my ears are burning".
Hi Vorpar. Thanks for your answer.

What does my ears are burning mean? Why burning? what is the origin?