三人行，必有我师(焉)

(I love that English "finished" and "done [for]" have the exact same figurative meanings as 完!)
Yes! So neat. Also easy to remember!

Wiktionary's description of how 蛋 functions as a suffix: "suffix denoting 'person of certain characteristics,' usually with a pejorative tone,"
哈哈哈, yeah, I wonder if that's a very formal version of something like the English "you--!" or the French "espèce d'..." (which I only know from Tintin).

玩完 is new to me and I want to translate it as "played out," but your sample sentence suggests that wouldn't quite work... .