Tā zǒng bǎ biérén de shì yě dàngzuò zìjǐ de fènnèizhīshì.
He always treats other people's affairs as his own responsibility too.
Tips
usage
Often used to deflect thanks - 'this is just my job.' Compare with 举手之劳 (a trivial effort) which also downplays help but implies the favor was tiny rather than obligatory.
memory
分内 = 'inside one's portion (分)'. If a task falls inside your 分 (share), it's your 事 (business).
