And actually this is formal setting. Because you are talking publically here, to people who don't know you, to people that you don't know. To people with different knowledge of english language, different manners. Formal setting is THE universal one
Also, some people like to defend themselves by saying that there are many people for whom english is not first language, so we can't expect to speak perfectly. I will just say that because there are many people for whom english is not first language, those who can use it correctly should do so, so that those people have easier time understanding / learning it.