to slack off after a period of doing a reasonably acceptable job in an activity.
athletic kid: come on! only 5 more miles!

fat kid: fuck that!

athletic kid: dont let up on me now!
by domiyan November 28, 2012
When you expect worse than what actually happens. A pessimist's let down. Can cause happiness and joy, or the anger and frustration brought by a let down.
I seriously expected to do worse on my test. God, what a let up!
by aslan8 December 15, 2005
When a person pretends to be your friend by calling you so he/she doesnt have to see you, opposite of lets hang out sometime. Very common between to people who just broke up. Will last until both parties have got the point that in a relationship their cant exist platonic friendship.
lets catch up sometime, il call you; or you can call me.
by sarkosy April 7, 2008
“Let’s do it”, is super vague and may have negative connotations. Therefore, “let’s do it up” is used as a phrase to prelude to a situation that will only result in a positive uplifting outcome.
Can’t wait to go clubbing tonight. Let’s do it up boys!
Big game today but let’s not let the pressure get to us. Let’s do it up!