He always butts into other people's conversations; he's a real meddler.
A buttinsky showed up during our date, so we couldn't be alone.
おせっかい refers to meddlesome behavior or a meddler, often with a nuance of unwanted kindness; お邪魔虫 is more about intrusive presence.
Standard kanji spelling using 邪魔 (nuisance) and 虫 (bug/person).
Mixed kana-kanji spelling; common in casual writing.
Compound of お (honorific prefix) + 邪魔 (nuisance, hindrance) + 虫 (bug, used figuratively for a person with a certain trait). The exact origin is uncertain, but it likely arose as a humorous, colloquial expression.