This expression is used in Italy when something hurts a lot.
It's an insult to a Divinity, more exactly to Mary, the mom of Jesus, comparing it to a dog.

Similar to "Madonna puttana" or "Madonna bocchinara".

It isn't suggested to say this to someone that believe in Christ.

Less used than "porca madonna" but still used.

References: Germano Mosconi.
"Ho preso 3 di fisica, Madonna cagna!"
"Quando cazzo puzzi, Madonna cagna!".
by DD3Boh June 5, 2017
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Usually used to say to a girl that she looks good (or sexy)
Oggi sei madonna cagna! <3 <3 <3
by Drink my sperm February 23, 2017
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