It was a bad call preflop by the other donkey.....but what do you want him to do on the flop? I didn't see the hand or the previous hands but if he put you on AK or pockets then it wasnt that crazy. Don't take it so badly when you get a suckout because I'm sure you've made some questionable calls and ended up getting lucky in the end. Just realise that his A4 off won't always crack your JJ.
Good luck to you and don't forget internet pocker = a lot more hands dealt/hour which results in more bad beats!