This reading of the kanji is unique to this meaning of the word, so here's a mnemonic to help you out!
The taste is so bitter tasting that you fall to your knees really, really hard. Luckily, you were wearing your knee guards (にが). Feel the relief that you were wearing them. Ack, no relief now. It's still bitter in your mouth.
This bacon is a little bitter.
This medicine is very bitter, so brace yourself!
Be careful not to let the caramel burn or it will taste bitter.