Wally on page 319
Apparently Ash is still hurt that Charlie didn't remember that he kissed her while he was feverish... She doesn't seem upset about the kiss so much as about his not remembering he did it. Yes, that hurt her, but give the kid a break... he did it while he was in a fever; that is sick and he was asleep... In any case. I think Kate is being overly harsh about what her brother was like. So far, based on past actions, Charlie doesn't seem to be rude or cruel and maybe only a little bit annoying. If that was really how Sam and Johnny were to Kate while growing up, then maybe the catalyst of the 'rude, cruel and annoying bug throwers' wasn't Sam/Charlie, it was Johnny... Kate's husband to be.
-
Just thinking that without Johnny in the equation, do to the time travel thingy, Charlie might have a chance to be a nicer boy to the people (girls especially) around him.

Joseph on page 319
@Davely, @Nezumi, et al:
Also, from the About page:
"
Kate
Charlie's kid sister. Something of a wet blanket.
Full name: Kate Julie Innow
Date of birth: 12th of December, 1993
Known secrets about her brother: 62, sorted alphabetically and colour coded by topic
Reason for marrying Johnny: Unknown, presumed malicious "
Also also, my personal take:
... because she seems to be a bit critiquing / fault-finding in others for her unhappiness, perhaps?
[my subjective interpretation. I try to take responsibility for my own unhappiness, not blame others, and still build mutual caring+trust / find solutions that both me and others are good with.
(hint: It's not easy, because humans are animals that still tend to evaluate others' undesirable behavior as
"Alert! An external, uncaring threat to my wellbeing is in front of me! attack/defend/avoid".
My brain is not exempt from this; I am just as animal as the next person... and i try to keep this in mind, and practice emotional intelligence.)
]

Joseph on page 319
@Wally
Yes!! +10
also: i just realized- Sam (older self) has been a bit... well, like, he's played practical jokes on Charlie (younger self), seemingly for the lulz. Not exactly in a cruel/malicious way... just... idk, not really recognizing / being cognizant how much it can hurt others.
Reflecting further, I'm guessing that:
i) their (Sam and Kate's) parents weren't really tuned into what their kids were doing / what their children's life experience in realtime was like (e.g. emotional experience);
and
ii) that that, combined w/ Sam's not-really-being-clued-in-either (wonder where he picked that up from? :o), led to some pretty deep hurt / unmet needs in Kate, => bitter resentment.
If it were me, I'd probably feel the same way.