Milsim with random patches and name tape doesn't catch flak.
Milsim with recent issue uniforms and unit patches (un-earned) on an adult may generate a poser alert, depending on the environment. When there are real vets wondering around in uniform at a non-Milsim game, it's a little inconsiderate. At a Milsim game, people may still separate you in their minds from the vets anyway.
When my son was 11, a friend in the US Border Patrol gave him a patch that I let him wear on his woodland jacket. It was pretty obvious he wasn't claiming anything. We did get a few worried looks though.