The sound of somebody popping their fingers, created solely by synthesizer hardware or computer software synthesis -- not all unlike how synthetic clapping, synthetic cans, synthetic car horns, etc. are produced.
Kat McSnatch's song, "I Don't Like You" is terrific, but it would be even better if it had synthetic finger popping it instead of real finger popping.
*knocks on bathroom door*
Him: baby, quit Finger popping your asshole! We are going to be late!
Me: ...Just getting out of the shower...not at all ready.