thoughtless; inconsiderate

Pronunciation:
in-KOJ-ih-tant

In a sentence:
When his co-workers realized that Harold hadn’t contributed to the birthday fund for the past two months, they called him incogitant and misanthropic, and conveniently forgot his own birthday as he sat at his desk and cried. 

In a different sentence:
Maria’s classmates didn’t appreciate how her daily gifting of apples made them appear incogitant by comparison; one day they decided to collectively purchase an enormous orange, which they felt would send a clear message.