The fact he and Chris (friend's oc) live together at all started as a haha funnee joke between us; so did the fact they own a turtle. It was basically like "lol Chris would totally bug Juniper about letting him get a turtle" "lol yeah" "haha wouldn't it be funny if Chris like murdered a turtle breeder and stole a turtle?" "haha yeah lol" "what if it was canon" "nOW WE'RE TALKIN-"
There's also the fact that Juniper hates mentos, that was a one time joke because i told my friend i nearly choked on a mento; to which they promptly went and made an artwork of him from in a sketch page, and uh i just kind of kept that as a thing, he doesn't like mentos and feels resentment whenever he sees someone eating them because he knows they're evil.
EDIT: I JUST REMEMBERED THE BEST JOKE WE MADE CANON-- Chris got blood in Juniper's car one time and ever since that day he has to ride in the trunk.