I wouldn't consider just walking past him mean, but I of course don't know what it's like in England.
Kicking him is too unrealistic, but I of course don't know what it's like in the US.
Well, don't take it as an English view. I used the word mean since it's not the nicest thing to do. I guess Rude would've worked. If you know what I mean. It's not nice, since you're not helping him even a little bit, but it's not terrible since you're not making him worse. I guess really, you could class walking past as neutral, and giving a penny as rude, since you're essentially giving him nothing and in a way, mocking the idea of helping him out, which is actually nastier than doing nothing.
And I wouldn't consider kicking a homeless guy realistic either, mainly since it's a crime. Unless it is a common occurrence in America where homeless people just get kicked.