I like to think that maybe sometimes Sirius didn’t remember whose shirt was whose in the dorm and so sometimes came down to breakfast in a quidditch jersey of James’, and one morning he does this and so does Lily (for an entirely different reason) and they kind of just look at each other like “well…”
Sirius wore EVERYONES clothes.
Remus’ sweaters
James’ jerseys
Peter’s muggle band tees
Marlene’s crop tops
Lily’s jeans and occasionally her skirts.
Sirius is a clothing thief.
and people will grow upset because all these clothes fit sirius better than themselves.