Tyler says Tiff had been talking about buying the new ride -- a Tesla Model X -- but complained there was no time in her schedule to do the whole car shopping thing. Well, that's what friends are for, apparently ... 'cause TP did the dirty work for her. Or more likely, an assistant did it for him, for her.

Anyway ... Tiffany wins!

Tiff is known for being frugal ... her love of Groupon deals landed her a gig as their spokesperson, and she once said she'd never own a nice handbag till she could keep it full with as much cash as it was worth.