Mandy - biffles, and life partners and annoy the shit out of each other. You know how it is. She's still finishing her healing training, so not properly employed yet, but I'm sure Roger can find plenty of reasons to pick on her.
Gwendolyn Montgomery - She's 3 years younger than him, so I doubt they'd know each other from Hogwarts, but she is very chatty and flirty, so she's probably talked to him a few times. She's an actress, so probably no personal interaction, though she says she is very good and he should totally have seen her on stage.
Theodore Nott - He works at the Ministry, so they would run into each other at times. He's a Hit wizard, who finished his training last summer, and I imagine there might be some sort of overlap there; he's not very talkative, but he'd be nice enoughh, at least.
Megan Jones - Bubbly, chatty and a muggleborn. If she thinks he's not a threat, she might talk to him. At the moment though, she's stuck at St. Mungo's having been unconscious for the best part of a week. She's a design student, and doing a bit of interning and such in Diagon Alley.
Marcus Flit - He's 2-3 years older, so not mugch there, but he was on the Slytherin team for quite a few years, so there could have been some sort of a rivalry there. Marcus lives out in Falmouth, and plays for the Falcons, so he thinks he's a really big deal, and can be rather annoying about it. They could have the occasional point maybe?