Well, you should really take two things into account:
First of all, when people say that, it means that yes, they've been lagging all day, and they sincerely apologize for any interference it might cause with you and your KDA, but they sure as hell don't have the patience to wait for their ISP to stop throttling their connection. I know this as I myself will typically tell people as the match is starting that my internet is not working properly tonight, it's out of my control, and I apologize in advance for any mistakes I make that are seemingly easy to avoid. We simply have tried everything to fix the issue, and have lost the patience anymore to try and fix it; unfortunately y'all just have to deal with it. If you want to be mad at someone, be mad at Riot and/or our ISPs making it impossible for us to enjoy the same things as everyone else does.
Secondarily, if you haven't been in the same boat as we have, then you cannot begin to fathom how frustrating it is. When every single action you make (which you and only you are responsible for) is delayed to the point where there are people you have the potential to save, but can't because of your connection, it sucks. It's not just frustrating for you, it pisses us off too.
I'm sorry on behalf of all of us with horrendous, unfixable internet connections that have caused any interference with your games, and I sincerely hope you recognize that it's terrible for us to endure as well, and most (if not all) of us simply cannot solve the issue without moving into more populated areas with more options of ISPs.