It's ok to give a guy some props if his workouts have been going well, but comments should be brief one-liners and this should not be done more than once per month, maybe twice in rare cases.
It's also ok to give a guy shit if he 'primps' before a date with a woman. You don't really think he looks good (to you), but you acknowledge that the dirty bastard has cleaned up well for his girl. Breaking a guy's balls in that situation is a must, especially if your lonely ass does not have a date that night.