Disturb and Be a Pain

Disturb

If you interrupt the quiet in a room or the rest of someone else, you disturb it. It can also mean to puzzle or trouble.
Ex: Linda wears an eye mask and earplugs to bed so traffic noise and her nightlight will not disturb her sleep. As a result, she gets a good night's sleep.
Ex: I find my neighbor's behavior disturbing. He sits on his front porch and uses a telescope to spy on the family across the street.
Do not disturb are the words on a sign you might find hanging on a hotel room door. To rock the boat is to disturb a situation that is fine just the way it is.
Ex: The maid should not enter to clean a hotel room with a Do Not Disturb sign hanging on the doorknob, as the guests may still be sleeping.
Ex: The sale of our seasonal merchandise was going nicely when one of the associates came up with a new idea for a television ad. We told him not to rock the boat.

Be a Pain

If you are a pain, you are an annoying or troublesome person. You might be called a pain in the neck. A task can also be a pain if it is unpleasant or difficult.
Ex: Taking our dog, Roscoe, for a walk is such a pain because he wants to stop and smell every tree and rock on our route. As a result, we all are reluctant to take him.
Ex: My twin brother can be a pain in the neck. Sometimes, she pretends to be me when she answers the phone and then changes the plans I've made with my friends.
Taking great pains while doing something means that you are very careful and pay close attention to detail. People who exercise regularly say, "No pain, no gain." It means that you have to work hard to get something, so if you don't feel some pain after working out, you haven't made any progress.
Ex: My mother takes great pains with her appearance. She never leaves the house without her hair in place and freshly applied makeup.
Ex: If "no pain, no gain" is true, I must have gained a lot from yesterday's workout, because I am in so much pain I can hardly move.