rude
怭 centers on a disrespectful, coarse attitude: rudeness or insolence in behavior.
怭 combines the heart radical 忄 with 必, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with rude or insolent behavior.
The heart radical 忄 suggests emotion, and 必 looks like a heart pierced by a line. Imagine a heart that is closed off and dismissive, leading to rude behavior.
For ヒツ, picture a rude person hissing at others: hiss -> ヒツ, and the heart 忄 is full of insolence.