Let down

Defraudar - To dissapoint someone. Let someone's down.

Example:

You're invited to the business meeting , don't let me down - Estas invitado a la reunión de negocios, no me defraudes.

In colloquial Spanish we say " Quedar mal " - Don't let me down - No me vayas a quedar mal.

to put one's foot in it

Meter la pata. - When someone says something that shouldn't have said and cause a problem for not be quiet. To put one's foot in it

Example:

The organizer of a party forgot to invite Jessica. The next day Tom, a friend of her, put his foot in it, and now she has a chip on her shoulder. - El organizador de la fiesta olvidó invitar a Jessica. Al día siguiente Tom, un amigo de ella, metió la pata, y ahora ella está resentida.

Another way of saying Meter la pata could be "regarla". Example: La regaste - You put your foot in it.