Rihanna may have turned up to the Met Gala looking unreal in a canary yellow gown by Chinese designer Guo Pei (rumor has it it took seamstresses two and a half years to make), but there are still lessons to be learned from last night's Met Gala which don't require spending a wad on a couture gown. From entrance to exit, here are six hacks from the hottest girls that hit up the all-night high-fashion rager…