I agree with Andi and Peachey. The only point I would like to add for the benefit of learners is that there is a limited number of nouns or phrases we can use with "rubbing shoulders". Examples: rubbing shoulders with the hoi polloi rubbing shoulders with the rich and famous rubbing shoulders with the great and the good "Rubbing shoulders with the mass humanity" does not sound natural to me. Perhaps it may sound better if it is written without the "the" - " "rubbing shoulders with mass humanity". "Rubbing shoulders with the masses" is OK (only just). Native speakers normally use a more colourful phrase with this construction. For example, "I am not interested in rubbing shoulders with the great unwashed of the land." So be careful when you use "rubbing shoulders with". It's not just a matter of putting in the name of a category of people. It's a device that requires skill and flair.

You should give us some context for phrases like this. Anyway, the expression is, "to rub shoulders with (group)". This means that you spend time and interact with the people in that group. You can also say "to rub shoulders with the masses", to mean that an upper-class person spends time with the common folk.

It means to be amongst people in a crowd. So, if you go into the street and there are a lot of people around you, you will be "rubbing" shoulders with them. Usually, we use "rubbing shoulders with the mass of humanity" in a negative way (people are dirty or have bad manners), or to explain that a rich or famous person has mixed with the common people.