Behaving in a particular way (which is specified before "mode"). Watch out, that kitten tends to nip people when she's in her play mode.Don't try to talk to Nate today—he's in his angry mode.
in one’s something mode
phr. behaving in a specified mode. (The something can be replaced by work, sleep, hungry, angry, etc.) Todd is always in his play mode when he should be working.