The guests were all talking about things that had nothing to do with me.

had 是动词 have 的过去式，表示"有"或"经历"。 nothing 是代词，表示"没有任何事物"。 to 在这里是介词，表示方向或关系。 do 是动词，意思是"做、进行"。 with 是介词，表示"和...一起"或"关于"。 had nothing to do with 是一个固定短语，字面意思是"与...没有任何关系"，表示"与...无关"。