unwelcome person; third wheel; interloper
Refers to someone whose presence is felt to be unnecessary or a nuisance, often in social situations. Can be used self-deprecatingly.
We want to talk just the two of us, so you're a third wheel.
Nobody talked to me at the party, and I felt like an unwelcome guest.
superfluous man (literary archetype)
A literary term for a character type, especially in 19th-century Russian literature, who is alienated from society and feels purposeless. Not used in everyday conversation.
The 'superfluous man' in Russian literature refers to a character who cannot find a place in society.
お邪魔虫 is a colloquial, slightly cute term for someone who intrudes, often used self-deprecatingly. 余計者 is more neutral and less playful.
Compound of 余計 (yokei, 'extra, unnecessary') and 者 (mono, 'person'). The literary sense is a calque from Russian 'лишний человек' (lishniy chelovek).