大陆马子大众凯子

It seems a very casual phrase using internet slang, where ‘大陆’ (Mainland) might represent the cultural background; ‘马子’ can mean 'girlfriend', and ‘大众’ for general or ordinary, and ‘凯子’ sometimes refers to a kind person (usually male) who always gives help to others without expecting any reward. As a whole, it's quite vague and informal, perhaps implying someone as common but good-natured from mainland China.