INTERLOPER

[noun] [C] [disapproving] - someone who becomes involved in an activity or a social group without being asked, or enters a place without permissionSome mothers angrily reported being made to feel like interlopers when they set foot in the school playground.National borders will become blurred as more and more foreign interlopers move into their neighbours' most profitable businesses.The security did not prevent an interloper getting on to the stage at the opening ceremony and making a speech in support of the local farmers.Why these interlopers selected this farm is unclear, but their simple robbery was to go horribly wrong.