The porn video tag "sex-friend" seems to be a combination of two words: "sex" and "friend." In the context of adult content, it is likely referring to a scene or video where friends engage in sexual activities together. This could involve any number of sexual acts or scenarios between individuals who are already acquainted or friends prior to the event. It's essential to note that this tag doesn't necessarily imply any particular type of friendship (e.g., platonic, romantic) but rather highlights the aspect of friends participating in sexual activities together.