I've heard about more than one person who had to buy a new cell phone because they dropped theirs in a toliet. Now logically, it was most likely in a pant pocket and it slipped out of the pocket during the clothing "transition" time.

I'm riding the bus more and really don't enjoy hearing a conversation - even worse, hearing both sides because the phone's volume is up so high. 

If I'm with other people and have to take a call, I'll generally pull myself away from the group to have the conversation - a. so they don't have to be subjected to it and b. so I don't have to see their faces as they wait for me.

Not in the bathroom, not while we are sitting down for dinner, not when I am in a check-out line - I think it is so rude to be on the phone instead of making polite small talk with the cashier.  Also - not in stores/boutiques at all. I will step outside. Not in restaurants at all either. Step outside.

Oh and you know another one?  Not in your doctor's office.  They are not there to watch you chat on the phone.  Just shut it off or ignore it and call back later.  That one really gets me.

I am all about SMS in public places.  if you really have to talk to someone that important step outside. 

I try to avoid it when I am a passenger in the car.  I am sure the driver and anyone else that happens to be in the car does not want to hear my conversation.

No cell phones for me when I'm:

eating with my family

in a store

or while visiting with friends.

I hate when women are on their phones in the locker room. And I agree with Rachel, when you are riding in a car (or even just walking with someone) it is particularly rude.

Totally agree with the locker room. Something truly awkward about it.

My husband is the KING of taking calls when I'm in the car with him. Not to mention we'll park the car at our destination and he'll sit there and finish the call (which is not always a quick 30 seconds...) HUGE pet peeve.

Not in the bathroom, at the dinner table, in a quiet public setting, inside a restaurant,when you're going through a cashier till, or when you're ordering something,

Not with the volume up. not yelling. not extended. I could go on ad nausuem.

Not in the check out line of the grocery store! Seriously, just hang up and pay for your groceries...all the rest of us in line are just staring at you.