"I AM UNWORTHY"
St Peter requested to be crucified upside down because he was UNWORTHY to be crucified like his Lord, Jesus Christ.
Since then, the inverted cross has became a sign of humility and unworthiness before Christ by many Christians especially Catholics.
More recently, It's been a trend for many to use this is the wrong context as "anti-christian."
But the truth is, God sent his son, Jesus Christ, to die for each and everyone of us on a cross so that we may live. A gift.... and all we have to do is accept and believe. Certainly, a gift that none of us deserve. And for that WE ARE UNWORTHY.