Is it rude to knock a bathroom door to determine whether it's occupied? My co-workers always try & open the door instead of knocking which seems much ruder to me.

You're right.  Knocking is better etiquette in my book.  Trying to get in seems a bit pervy.

I like the knocking too.

I'm not Miss Manners, but a locked door is the best sign of the room being "in use"---and it doesn't attract attenion.

Look at the Lock. Or Knock First.

It's better to knock first, than just trying to barge in.

If the door is closed and we are in doubt, we knock.

After we are done, lights off and the door is left wide open.

Perhaps you need a sign on your door. ~ got paper, marker and tape ?~