The trade was maybe a little lop-sided in your favor. I'm assuming you meant Brian Roberts, here. Roberts puts up good numbers at a position that is scarce on talent. Rios may have similar numbers to Roberts historically, but you expect better numbers from your outfielders than the kind of numbers Rios has been putting up. 32 steals last year is not bad, but I would like to see a better BB:K ratio. Roberts is off to a hot start and Rios is rather cold at the moment. That makes it even a harder sale. Kershaw is a hot commodity right now. He's a young, highly touted player with huge upside.
All of that aside, this other player didn't need to be abusive. A simple email saying that it wasn't a good offer would have been just as easy to send. Some people are just, well, I'm sure you can come up with a good term on your own.
Personally, I am horrible at figuring out what is a good trade offer and what isn't and I've been play doing this for a few years. I don't often make offers for fear of looking the fool. It has probably kept me from doing better in my leagues. Don't feel too bad about it. Learn from it and keep plugging away. Do your homework on the stats and maybe check out the trade forum and read through some of those posts and see how other people evaluate trades. Seeing other peoples perspective on things can help out. Hasn't helped me a whole lot, but I'm thick...
Good luck and remember, it's only a game. Don't let someone else ruin the fun for you.