The term 'prim and proper' often denotes an outdated or conservative style, potentially overly strict. Her grandmother's prim attire made her look as if she had come from another era.
Pro Tip 2/3
Emotional Distance
'Prim' can imply that a person is not very warm or approachable, due to their formality. Despite his prim demeanor, he's very kind once you get to know him.
Pro Tip 3/3
Visual Impression
When describing appearance, 'prim' suggests neatness and simplicity, avoiding flamboyance. The job interview called for a prim suit, rather than a flashy ensemble.