Jim: Have you decided who you're going to vote for?
Chris: I still don't know. I'm kind of on the fence right now. Both candidates are qualified and seem great for the job.
Carol: Have you and your husband found a new apartment yet?
Shelly: Well, we're still on the fence about which city to live in. I want to live closer to the beach, but my husband wants to live closer to his work.
MEANING: to be on the fence means that you cannot make up your mind between two choices or alternatives. It means that you are having a hard time deciding on one thing over the other.
Tom: Man! Chrissy must have woken up on the wrong side of the bed today!
Steve: I know. She is in such a bad mood.
Tom: I think I'll just stay away from her today.
Sara: Jenny, can I borrow a pen? I forgot mine.
Jenny: Really? Again? You always forget your pen. How many times has it been now? A million...
Sara: Wow! Somebody woke up on the wrong side of the bed.
Jenny: I'm sorry. Yeah, I'm a little stressed out today. Here you go. You can use this pen.
MEANING: to wake up on the wrong side of the bed is an expression used when someone is really grumpy or in a bad mood. It is almost always used with a past tense form, like in example #2.