Contrary to most of the definitions found here, this is the correct one:
'ILL' : Adjective meaning 'wild' or 'crazy'. Not always derogatory, but used when something may be so outrageous so as to be unruly.
'ILLIN': Adjective or Verb. Lunatic behaviour. See above.
To get shitty or get an attitude with someone. or to be bitter and pissed off, angry, especially when showing disrespect or after been disrespected or humiliated or getting fucked off