interlope

This verb carries a strong negative connotation of intrusion and social impropriety. It describes an action where someone enters a space, conversation, or relationship where they are not welcome or have no legitimate claim to be. The feeling is one of overstepping boundaries or violating a social contract of privacy.

In modern usage, it is significantly more formal than "butt in" or "interfere." While "interfere" often implies actively changing the outcome of a situation, "interlope" focuses more on the act of unauthorized presence or the presumption of having a right to be involved.