When your arm looks like a funnel because you're a weak little bitch. Look in a mirror at your profile - if you don't see any seperations, striations or definition and your arm smoothly tapers from your shoulder to your wrist...yep, you've got a bad case of funnel arm. Generally brought on by complete lack of strength, total avoidance of the gym and being generally a fat blob.
What was he thinking when he put on that cutoff shirt? Someone should tell him to cover up those weak ass funnel arms. Dude needs to hit the gym, that's just embarrassing.