Doing good and being good is a wonderful thing. Your life is made up of the decisions that you make each and every day. If you consistently make good decisions, you will grow as a human being and will be a net benefit to society at large. This doesn't mean that making good decisions and doing good deeds will always bring beneficence to you; you can most definitely do the right thing and die for it that is the unfortunate nature of this fallen world. Still it is well worth your while to be true to yourself and to be a virtuous person of good heart, good deeds, and good faith.
What, however, is an annoying do-gooder? An annoying do-gooder is someone that insists that they know what is best for you and to show their conviction of that attitude, they will do everything within their power to compel you to conform to what they perceive to be the right behavior for you. While the intent may be to improve that person's character and to straighten out that person's ways, unfortunately that vision often comes from someone that has "a beam is in thine own eye." (Matthew 7:4).
To make matters worse, do-gooders have taken to changing the game from simply one-to-one consultation, whether desired or not, to utilizing the force of government to compel so-called right behavior from recalcitrant individuals. For instance, while there may be valid reasons why people that smoke should not be allowed to do so inside buildings in which the ventilation is inadequate or the like, it makes no logical sense that people can't smoke outside in the open air. The do-gooders will claim it's a health hazard but there appears little or no hard empirical evidence to support this accusation, and if you allowed this fallacy to be swallowed, than where do you draw the line as there are probably an infinite amount of activities that people engage in that are both annoying and possibly harmful.
The do-gooders of today's world want you to conform to their particular brand of group think. They want you to listen to their music of choice, dress like they do, talk like they do, visit and frequent the places that they do, weight the same weight as them, think like they do, and be just like them. That's silliness of the highest order but to makes matters worse, the do-gooders will stop at virtually nothing to see that their thinking is the law of the land. That is why each year we have more and more laws that circumvent our freedoms, our choices, our desires, and our free will.
People will make bad decisions that are obvious to us, and probably are just as obvious to the people making those decisions. That is their choice, as a good neighbor we can help them to see other choices, but ultimately sometimes you must first do the wrong thing before you can learn how to do and desire to do the right thing. We call that behavior: free will; the do-gooders, however, are the opposite of free will, they are our regulators.