Off On The Wrong Foot: Getting a bad start on a relationship or activity
Example: He got off on the wrong foot by under estimation of this business.
On Cloud Nine: extremely pleased or happy
Example: Ann should have that job successfully, she seems to be on cloud nine these days.
On pins and needles: Anxious or nervous, especially in anticipation of something.
Example: John has been on pins and needles all day, waiting for his wife to have the baby.
On The Fence: not able to decide something
Example: Always, I am on the fence at the ice cream counter, chocolate or vanilla.
On Top Form: in good physical condition
Example: I'm not good in this morning, but he looks on top form.
Out Of The Blue: Something that suddenly and unexpectedly occurs
Example: One of them wrote to us out of the blue several years later.
Over My Dead Body: not allow something to happen
Example: Are my children going out to the dance party tonight? Over my dead body!
Over the top (OTT): too extreme and not suitable, very expensive
Example: I thought the decorations were way over the top.