If Old Man Marley from Home Alone is actually a nice man then why does he always give Kevin a cold and creepy stare (particularly when Kevin shouts that he's not afraid anymore)?
He doesn't give that cold and creepy stare, he looks like so.
Kevin's brother has told stories about that old man the he murdered his family with snow shovel. This is the reason why Kevin gets scared of him, shouts after seeing him and tells him that he is not scared.
Buzz: Check it out. Old man Marley.
Kevin's Cousin: Who is he?
Buzz: You ever hear of the South Bend Shovel Slayer?
Kevin's Cousin: No.
Buzz: That's him. Back in '58 he murdered his whole family and half the people on the block with the snow shovel. Been hiding out in this neighborhood ever since.
Certain people may appear creepy by their looks or because you might have heard stories about them, but you cannot know them if they're nice or not until you talk with them or see them doing things that may make you sure that they are not nice.
This was the same case for Kevin as well. Kevin is a kid and he is easily scared by the people appearing creepy just like that lady in Home Alone 2.