Kelsey Grammer is seriously lacking in the man department -- at least according to his ex-wife Camille ... who STRONGLY insinuated yesterday that the actor has a small penis.

In a recent promo for "Real Housewives of Beverly Hills," Camille describes Kelsey ... "Big hands, big feet, big disappointment" -- and last night in New York, she said it's true ... telling us, "It was a lot like that. I had that for 13 years, unfortunately."