THEME:   four long answers have words starting with K and P   
GOOD ONES:     Military mess assignment {& theme}   KP-DUTY   
Bit in a horse's mouth?   OAT      
BTW:   Queen's spouse   KING [my candidate for the most pedestrian clue ever]      
Four pairs   OCTET [just a week or so ago I pointed out that an octet is not comprised of a series of pairs but 8 distinct people or things --- alas I am tossing pearls to … deaf ears (doubt they'd be bothered by a mixed metaphor if they can't define properly the words they choose)]      
Conceded the point   BACKED-DOWN [a bit tortured clue since merely conceding a point does not mean one has backed down from it]      
Song for three   TRIO [I liked the use of this less popular definition; doesn't have to be Il Volo]      
RATING:  
 
   Three grins = Loved it; Two grins = Enjoyed it; One grin = A bit bland for my taste; One teardrop = Not much fun