Normally you would say "estás loco". This indicates mood or state of mind, hopefully temporary. If you say "eres loco" it indicates an intrinsic, permanant characteristic.
Bésame el trasero that's how u say you are crazy about me
loco
You can say "Estoy loco(a)".
You say, "tortuga loca."
¿Eres loco?
Estamos locos
Me vuelves loco/a.
No estoy loco
no demente, desquisiado, son others ways to say crazy.
You could say "Sombrero loco".
"piernas locas"
hermana loca