IPA: /ˈʃɜːrtiər/
KK: /ˈʃɜːrtiər/
More irritable or easily annoyed than someone or something else.
After a long day at work, he became shirtier than usual when his friends teased him.
The word 'shirtier' is derived from 'shirt' (from Old English 'sceort', meaning a garment worn on the upper body) and the suffix '-ier' (meaning one who or that which). Thus, 'shirtier' refers to something that is more characteristic of or related to shirts.
Think of a 'shirt' as a garment and remember that 'shirtier' means more like a shirt or having more qualities of a shirt.