"madonna troia" is a tipical italian angry expression which is used when you are really angry and u wanna shout to the gods to know how much you are angry. Especially in Veneto, we use to say it really often, even if we are not angry at all because it's almost a fashion. So if u come and visit italy, you can spam it as much as you like it and you will make lots of friends in few seconds. Trust me, this is pure pwnage.
*TIP* If you are really angry, u can say "MADONNACCIA TROIA", or with even more effect "LA MADONNACCIA TROIA".
"OH MY GOD I'VE BEEN ASKING ADSL FOR 4 YEARS BUT I STILL HAVE NOT IT, MADONNA TROIA"
"Ma dio cane son 4 anni che chiedo l'adsl e devo ancora averla, madonna troia"
"It's raining like hell, Madonna troia!!"
"Madonna troia che piova!!"
"Mi si è bucato il goldone Madonnaccia troia"
"Oh my god the condom has a hole Madonnaccia troia!!!"