So I guess this is a gag based on Mami having some "old-fashioned" tastes that're about a generation or two out of sync with the others, such as in post #1271542. Seems to be a theme with rifyu's Mami.
Wow, a mustache T-shirt!I'm so jealous~Hey Madoka, check this out.Since it's you, Madoka, I'll even throw in Tatsuya's.I'll give ya one if you make a contract.Eeh~ What should I do~Hey Mami-san, check this out.My, isn't that a Haga-chan T-shirt?Wha? Haga-chan? Madoka, do you know what that is?Eeh... never heard of it.N-never mind that, let's go eat!