Lois made a science out of spying.
Which makes it in-character for her.

Though in her defense, I don't think she's all that guilty in the two instances named. When she spied on the Mayson kiss, she had approached the door for an innocent reason and almost couldn't help seeing what she saw. She didn't go there for the purpose of spying on Clark. And when she followed him to the jewelry store, he was in
public. Granted, she'd have probably spied on him in private if she could have found a way, but watching someone walk down a street isn't quite the same as hovering outside his windows.
Still, I agree that Lois had fewer scruples than Clark when it came to spying, so I'm not jarred by it when she does something like that. It's far more in-character for her.
With Clark, in the pilot at least, it just
isn't to me. He didn't know either Lois or Luthor well enough to be sick with worry over their date, and there is no reasonable explanation for him to be hanging around outside her third/fifth story window eavesdropping on her conversation with her sister. I can't find it in me to romanticize that, and I can't find it in-character for Clark, either.
"Squick" is fanspeak, I'm afraid - one of those terms that has, for better or for worse, made its way into my vocabulary. I believe it's a combination of the words "squirm" and "ick". If something squicks you, it makes you uncomfortable or repulses you. Squicky is the adjective form...and apparently I find peeping toms squicky!
Caroline