Let oneself go

To become less constrained.I went to the party and let myself go for the evening.

Let one’s emotions show

To be emotional (where it is not appropriate).The mayor let his emotions show when his plan for the new stadium was defeated by the city council.

Let on

To try to make people believe something, to pretend something.The man tried to let on that he did not want the job but actually he did.

Let the cat out of the bag

To reveal a secret."Don`t let the cat out of the bag about the surprise party for our boss."

Let (something) slip (out)

To tell a secret by accident.I let the date of the wedding slip out by mistake at the dinner party.

Let (something) slip by

To forget or miss an important time or date.We let my parent's wedding anniversary slip by without doing anything.

Let (something) slide by

To forget or miss an important time or date.I let my girlfriend's birthday slide by without noticing it.

Let (something) slide

To neglect a duty, to ignore a situation.Recently, I have been very busy and I have let my work slide.

Let (something) ride

To continue a situation without changing it.We should forget about the recent problems at work and let the matter ride.

Let (something) pass

To let something go unnoticed or unchallenged.I did not like what my friend said to me but I decided to let it pass.