السلام عليكم Brother, if such situation arises while in Jamaat, you should not keep things to yourself, rather upon your return from Jamaat, elders in the locality should be made aware of before the Karguzari. Elders will then give Targhib how to deal with newcomers or behave with each other. Moreover, these things are discussed before the Jamaat is sent out. Well, some brothers won't pay attention to the most important talk before the Jamaats go out. It looks like the person you mention is one of them.