Feigned is an adjective that means "not genuine," like your feigned interest in your friends' discussion of celebrity hairstyle trends.
The word feigned, pronounce "faynd," comes from the Old French word feign, which means "pretend, imitate, shirk." Feigned emotions aren't real, and therefore, they are a bit dishonest. You act like you care but you really don't. Maybe you are just being nice, like your feigned enthusiasm for your dad's woodworking projects — you know how much he enjoys it, so why not act interested?