I enjoyed this a lot! Severus and Sirius’ bickering was so much fun to read; I can just picture the miniscule Sirius in that crystal ball shaking his fist at Severus and getting suspicious about his motives. Don’t know why, but I really loved this line:
I remember you at school; bending over for any bigger boy who wanted you, and passing it on with interest to the younger ones.
I certainly had no trouble believing Sirius’ words, especially since your adult, "in for a Sickle" Severus displayed that delightful, opportunistic streak of his by seizing the moment with Harry. Sirius’ hilariously embarrassing warning had such a lovely, satisfying outcome. It's a pity he didn't get to see that. *g*