this nearly cant be translated. it means that you want to express a kind of "friendly jealous". So this sentence can be used only between good friends. for example, ur good friend expected a football as a gift. Today his father gives him a football as a gift. So ur friend is very very happy. Now you see him while he is happy. U know the whole story so u can say: (瞧, or 看,)给你美得. It means that you know that his wish has become true, so you are "jealous". But in fact, you feel happy for him. So we translate it as: oh, I am jealous! But it means that: I am happy for you. 瞧 or kan means: look! 瞧给你美得：look, I am jealous! or look!, How happy you are! I am so jealous! but the real meaning is: I am happy for you. 给 + somebody + verb + 得 is a structure that you can use when you want to highlight some emotion. 给 means "被" or “把”. it means "passive". this structure omitted the subject and the adj. for example, u make your clothes very dirty. then your mom say: 瞧给你弄得！ it means: "你的衣服被你弄得很脏。 the subject: 你的衣服 the adj: 很脏. both of them are omitted. it rests only "被你弄得" and we change 被 with 给. so it becomes 给你弄得! it highlights that ur mom is unhappy~~~~

瞧给你美得 literally: see? so glad due to you. 美 means good mood, fabulous.

What makes you so glad/pleasure/happy? What makes you （feel like ）satisfied?

当有人因为某事很开心时，你可以这样说，意思是‘瞧你多开心’，‘美’有时候指‘开心’，比如‘心里美滋滋的’