Because of [insert reasons] Martin's landlady gifts the house's occupants a big cake for everyone to share.
Martin spends all day in his van quietly looking forward to it, even if it's just a tiny little piece... except when he gets home he finds that the students ate it all without him, either because they just didn't think to include him, or else kind of sort of forgot he lives there too.

I'd prefer it if the students were a bit oblivious and didn't really notice that Martin was hurt by the exclusion far more than he was disappointed by the lack of cake.

Bonus MJN offers appropriately eccentric comfort.