This is when you have to conduct yourself in a professional manner as you are now representing a company/organisation.
When speaking to people (young and old), sending an email, or using the telephone, you have to refrain from using slang and always use professional and appropriate language.
Different cultures may use body language and gestures which are different to us. If for example someone avoids making eye contact with you, this could be due to a cultural difference. In some countries it is considered disrespectful to look into a senior persons eyes. Whereas in the UK, it is considered rude not to look someone in the eyes when speaking to them.