Interloper – Person who interferes with affairs of others, often for selfish reasons; or someone who intrudes in a place, situation or activity

(Pronounced in-ter-loh-per)

At the interval he always loped over (interloper) to the theatre bar and interrupted people's conversations to try impress them in the hope they'd buy him a drink. He intruded and interfered for selfish reasons.

Examples of interloper in a sentence

They couldn't seem to go anywhere without her husbands friend tagging along, she saw him as an interloper in their marriage. 

His mother was an interloper in his dating life, she was constantly trying to interfere with his date plans. 

They called the police when they found an interloper snooping around their property.