1. Arghhh! (first year)
The first time James Potter notices Lily Evans, (for he has always known her, but not noticed her), is when his second prank literally explodes in his face. Riding on the earlier successful debut prank he had pulled with Sirius Black, (who James's mother would have only stressed as Black), he had quite confidently planned his next prank, which in his opinion would assert himself in the history of Hogwarts. Nothing had prepared James for anything other than a success, so when an irate redhead pointed her wand at the lump of connected fireworks and made them explode in his face, quite accidentally, James could only yell as he backed away and bumped into a suit of armor which clattered on top of him.
For somebody who just made a bunch of fireworks explode in his face accidentally or not, Lily was surprisingly advanced and caring. Rapidly apologizing, she tried to heal the bump on his head with a few complicated spells as best as she could before pointing her wand at his forehead and muttering something.
This had all happened rather quickly, and James was left to himself to sulk alone in the common room. The sight of Sirius, Remus, and Peter jostling and joking through the portrait hole did little to lift his emotions, and the fact that they took one look at him and began laughing didn't help matters either.
Now James was blatantly sulking on the couch in the middle of the common room, legs splayed out, and lower lip jutting out. Sullenly telling them the transpiring of events that evening, he was met only by a round of guffaws.
Sirius, laughing as Remus and Peter rolled on the ground, choked out,
That must be why you have singed eyebrows that are dyed mustard yellow.
For the next couple of days, Lily Evans, who sat across from him in Charms refused to meet his eyes, but whenever she did, her shoulders shook with laughter.
After the spell wore off, and his eyebrows grew back, James had to acknowledge that that was about the time he started to have a crush on Evans.