Showing Serbian muscles is when you're trying look like a tough guy while in fact you're very week. Your muscles are those of somebody bigger than yourself but which you pretend as if you had them.
The saying comes from Serbia being in conflict with all other countries and peoples, pretending that Russia will help them out of any problem situation.

Micro marriging is when your partner manages your personal day-to-day tasks with you much like a Micro Manager at work.