If you reject your mother's offer to buy you a pair of lederhosen with a snort and eye roll, you are spurning her generosity. To spurn means to reject with disdain.
Originally, to spurn was to kick away. Though it's not used in that context so often anymore, being spurned still feels like a kick in the gut. You can reject someone kindly, or let them down easily, but you can't spurn someone with anything but malice.