Yes it is one of the major sins in the sight of Allah. Prophet Mohammad (S.A.W) said that people who adopt the customs of other relegions will be raised with then on the day of Qiyaamah.
hypocrite is a person who pretends to be good, pious or sympathetic without really being so. It is strictly sinful to be hypocrite. It brings you to the Hell Fire on the Day of Judgment after life....
A person who claims or pretends to be very moral and virtuous but who does not behave as such.
That would be someone who says one thing and does the opposite.
when someone tells you that they love your shoes (or something) and then you heard from a friend that the same person told her that she doesn't like your shoes. A hypocrite is someone who tells you...