A long horizontal slimy smear on the bottom of your Iphone caused from answering a call using the slide bar with a snotty finger.
Jake: Dude whats that slimy smear on your iPhone?
Kevin: Ahh dude, I have the flu (sniff, cough) that is just an iSnot from my snotty fingers (cough, sniff). Are you hungry? I will let you lick it clean for me? (cough, sniff)
Jake: Gross Dude (chuckle), iSnot interested your Swine Flu bodily fluids! May be you should use your elbow to use your iPhone!