He tends to go into his shell when he meets new people.
go into one's shell
idiomTo act defensively.
Origin
disputed originFrom turtles, who go into their shells to protect themselves.
Whenever the manager starts criticizing her work, she goes into her shell and stops participating in the meeting.
Rather than defending his controversial theory against the aggressive questioning, the professor simply went into his shell and refused to speak further.
- 01
abound in one's own sense
To follow one’s own inclinations and opinions.
- 02
ace up one's sleeve
A surprise advantage of which others are not aware.
- 03
act one's age
To behave in a manner appropriate to one's age.
- 04
act one's age, not one's shoe size
Synonym of act one's age (“to behave in a mature manner; to avoid being childish”).
- 05
afraid of one's own shadow
Exceptionally timid.
- 06
air one's dirty laundry in public
To reveal one's sordid secrets to the public.
- 07
air one's dirty linen in public
Synonym of air one's dirty laundry in public.
- 08
albatross around one's neck
A characteristic, possession, associate, or previous deed that hinders one's ability to succeed.