This milk smells off, this steak looks off- i.e. spoiled/rotten. Sometimes you'll see ot used with people but that doesn't mean the person is spoiled or rotten. It means that the personyou are off of is someone you don't want to spend time with.
Here's a good one- very idiomatic. He fell off the wagon. It means an alcoholic or sometimes an addict of any kind-but usuallly alcohol- has been sober (not drinking) and started drinking again.
I am taking off my shoes--Almost all clothing is taken off and Put on. I make my Second language students use the infinitivee form so to take off and to put on are infinitives you see 90% of the time when it comes to dressing.
She is off her rocker-i.e. She is crazy. I imagine it comes from people used to sit on their porches and in small towns everyone would know about the most intimate of details of all its citizens.
He gets off on watching porn. Idiomatic expression- self explationatory I hope
Get off the table, you dumb cat! Command:verb + preposition
The throw/catch was off by a hair. i.e. really close, almost.