1.
If someone picks on you, they repeatedly criticize you unfairly or treat you unkindly. ( INFORMAL )
Bullies pick on younger children...
PHRASAL VERB : V P n
2.
If someone picks on a particular person or thing, they choose them, for example for special attention or treatment. ( mainly BRIT )
When you have made up your mind, pick on a day when you will not be under much stress...
= pick
PHRASAL VERB : V P n