What does " who could you have possibly done? mean in the following context ?
Hi
how are you?

I would like to ask about the meaning of the sentence" Who could you have possibly done " in this context :

Here is the video from the TV-series "Friends"

http://130.211.5.232/yarn-clip/4759828b-0baf-48c0-ac0b-b14cd0c00a3b

This is the written context:

Monica: You invite my brother, you invite my whole family, and not me? Why? Why wouldn't you want me at your wedding? What could I have possibly done? Stuart.
Frannie: I believe you know my husband.
Ross: So it's really a question of "who" could you possibly have done.

Question

What does " who could you have possibly done?  mean in the following context ?
Hi 
how are you?

I would like to ask about the meaning of the sentence" Who could you have possibly done " in this context :

Here is the video from the TV-series "Friends"

http://130.211.5.232/yarn-clip/4759828b-0baf-48c0-ac0b-b14cd0c00a3b

This is the written context:

Monica: You invite my brother, you invite my whole family, and not me? Why? Why wouldn't you want me at your wedding? What could I have possibly done? Stuart.
Frannie: I believe you know my husband.
Ross: So it's really a question of "who" could you possibly have done.

Answer

"To do someone¨ can mean to have casual sex.

From the dialog, it appears that Frannie did not invite Monica to the wedding because Monica had had a sexual relationship with Frannie's fiancée.  [former lovers are not normally welcome at a wedding ....]

Notes - 
The humor in this dialog depends on a double meaning of ¨know¨ somebody and the shift between ¨what you did¨ and ¨who you did.¨

Frannie: I believe you ¨know¨ my husband.  
[intended meaning - you know him too well because you have had sex with him in the past]

Ross: So it's really a question of "who" could you possibly have done.
[intended meaning - Frannie is upset because of who you´ve had sex with.]

Answer

In the context “done” or “do” means to have sex with someone. I can’t watch that clip right now to confirm why he said that, but I’ve seen that episode.