fooling or deceiving somebody is a put-on.
You say David always changes his girlfriends...
come on~ that must be a put-on
To suddenly use a mask of superficial personality or emotion to cover your real one, around everyone or a certain people to make them either:
1. like you
2. dislike you
3. feel sorry for you, or
4. be downright confused.
Also can be referred to as two faced.
1. Jared is such a put-on when he brings me around his guys!
2. When she started crying and feeling sorry for herself, I could tell it was a put-on.