Just sitting in the tub while my wife bathes me like a small child.
It's so relaxing and I feel so loved. Especially when shes being really careful like you would with a child and talking to me like a baby. For me it's right up there with the experience of having your diaper changed by someone you really really love. The feelings of trust, love, and feeling vulnerable yet its not a bad vulnerable.
Think next time I try it, I will bring a paci and a few toys.