You're right, 'paddy' is used offensively too, it's funny but 'paddy' sounds vaguely condescending whereas 'mick' is just plain nasty. If you get called a stupid Paddy, it's bad, but if you're called a stupid Mick, it's really threatening.
People in Ireland do use the expression 'acting the Mick', Deano - they obviously aren't aware of how it's used abroad, and just think it's a fun expression. I don't think it's even a case of a group re-appropriating offensive words to use affectionately amongst themselves*, I think it's just lack of awareness.
*e.g. the folk group called 'Paddy Goes to Holyhead' - not actually a Frankie Goes.. tribute band, they just had fun with the name😂