i only ghost people who i know hate being ghosted. you get a better reaction when you're caught. "omg! exactly how long where you there?!?" is much more fun then "what the hell are you doing?" "um, ghosting?"
tip: if you want to ghost someone in a group of people, do something like wave or smile if the others notice you, basically just greet them normally but quietly. then nobody thinks you're doing anything weird. i catch my friend trying to get me back because she is way too obvious so anyone in front of me starts laughing.
we call it personal space invaders
we also rick rolled teachers but the only one we caught out just went along with it and kept pressing the windows in time with the song, thinking the class were idiots for dancing to it.