痴 molester

The molester acquires sick knowledge in his CHEESY exploits.

train pervert ★★★★☆ FR1/2 KANA
痴 (molester) + 漢 (Chinese) = 痴漢 (train pervert)

Usually 漢 means Chinese: it's used in a lot of obscure words ('Chinese dictionary,' 'Chinese herbal medicine,' 'Chinese classical literature,' etc.)

HOWEVER - aside from 漢字 - the only time 漢 is really used in daily life is here: 痴漢, meaning a guy who molests or gropes women on crowded trains.

So the literal reading is: 'sick Chinese' !WTF???

terrible at --xxx ★★☆☆☆
音 (sound) + 痴 (molester) = 音痴 (terrible at --xxx)

literally, to be tone-deaf, unable to carry a tune. But you can also say, 方向音痴, which means 'to have no sense of direction,to get lost a lot.' One more idiom: 運動音痴: (undou onchi) means terrible at sports.

grumble ★★☆☆☆ 1/2 KANA
愚 (dum diddy dum dum) + 痴 (molester) = 愚痴 (grumble)

grumble or mutter a complaint over and over - to bitch, whine, grouse, sing the blues. (as opposed to 文句 (もんく) which means make a loud and articulate complaint)