It's nice to congratulate people you know on doing something well, rather than a "well done you did better than..."

Not everything has to be a dig at someone else yknow, and a lot of the time it can make it sound like you're only mentioning someone doing something for the sake of getting the chance to insult someone else whether you meant it for that purpose or not.

Put your dislike for someone aside for once. Cheer on a friend for doing something good, for achieving something, there's no need to mention someone else bad in that. Your friends success isn't and shouldn't be based on whether they happened to do better than someone you dislike or not, it's based on them doing something very well, which if they have, you should be telling them this without any mention of someone else, cos that mention just detracts attention away from your friends achievement.