He may have had some run-ins with George Waterford, who is both in his house and a prefect! I also have two of his other housemates (Idunn Fraser and Holliday Fudge), but not sure how much they'd have to do with him.

Abraxas Crabbe is in his year and friendly as all get out, but also is a wealthy pureblood and best friends with Sirius Black so Rych might dislike him on principle xD