It means to be dishonest, deceitful or hypocritical.
lacking sincerity; "a charming but thoroughly insincere woman"; "their praise was extravagant and insincere
The word 'glib' means fluent but insincere.
He made a show of caring and wanting to help, but we knew he was insincere.
sincerely
The opposite could be insincere, or (for enthusiastic) unenthusiastic or unambitious.
lacking sincerity; "a charming but thoroughly insincere woman"; "their praise was extravagant and insincere
It means someone is insincere.
Insincere or ironic, mean
Your countenance belies your insincere request.
An insincere person should not be trusted
An insincere apology is no better than no apology. I noticed that she was insincere when she said the shirt that was too small for me looked good.
The word 'glib' means fluent but insincere.
He made a show of caring and wanting to help, but we knew he was insincere.
Insincere or foolish talk. Origin unknown, first known use 1929. meaningless talk; nonsense.
yes
No.
An actor is a player, one who plays a part in a dramatic production. The word is used figuratively to mean a person who seems to be playing a role, seems insincere.