"Mae o'n gas."
Translation:He is nasty.
Yes, it can mean 'it is nasty' and 'it's nasty'.
Both are listed as acceptable alternatives.
That was me - I added them earlier today, but probably after HW's note here.
hi. it wouldn't accept 'he is nasty' from me just now - because i missed the capital? it's usually not bothered about that.
Just checked, and 'He is nasty' is still the main answer along with the usual variants.