Until someone translates them directly on the pictures, here’s a quick translation:
Copain! : My Good Friend! (hyper-enthousiastic way, with a slight amount of dumbness in it)
Tu sors! : Get out! (after a real bad joke, or a useless remark)
MDR : LOL or, literrally: died from laughing.
Remonte petit topic : go up small topic, aka, bump!
pfffff… : sigh!
merci d’utiliser la fonction rechercher : please use the search function!
CCMV : Comité Contre la Modélisation de Voitures? Anti-Car-Modelling Comity.
Ciao
Dani