According to a tip received by SFist, Haus, a coffee shop on 24th Street, was recently privy to an important and strongly worded warning. A "Yuppie Infestation" is just now sweeping the area, according to the sign maker, and though Haus opened its minimalist doors in May of 2009, its strong coffee and wi-fi could render the not-quite-so-new shop a dangerous hot spot.