It is one of the more subtle ways of telling annoying bragging people to fuck off. You don't really mean it, nor you care about their success and you want them to get out of your sight or at least change the topic.
It can also be accompanied by 👍 (4fingers) 👉 gesture for maximum effect
Random Douchebag: Hey I aced that calculus exam the other day, still don't know how you managed to fail it.
You: Gud 4 U!(👍 (4fingers) 👉 )