“But as he which hath called you is holy, so be ye holy in all manner of conversation;”  
1 Peter 1:15

He says be holy in all manner of conversation; because you can. Conversation there actually refers to behavior, in other words express holiness in every behavior you have- where you are and whatever you are doing.
To be holy means to be consecrated and separated for a purpose, it is the purpose of a person or an object that makes it holy- it doesn’t mean wearing white or sounding a bit spooky, neither does holiness mean righteousness or sinlessness. For example, God appeared to Moses:
“Then said the Lord to him, Put off thy shoes from thy feet: for the place where thou standest is holy ground.”  Acts 7:33
How righteous was the ground? It wasn’t, but that place had been separated by God for a purpose and so it was holy ground. The Bible says:
“Wherefore come out from among them, and be ye separate… And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty.” 2 Corinthians 6:7-8
You are to live your life separated unto God and put away from your midst associations and counsels that are unbecoming and against the word of God.