The Rogatchover, Rav Yosef Rosen was famed for his genius and known also for his wit. He was once in his study with a close friend and famous Rabbi in his own right when a woman entered and asked The Rogatchover to bentch (bless) her. As he often replied to such requests he answered, “I am only a simple man, I bentch only after eating”. The visiting Rabbi then said, “Why not bless her? The Gemora in Brachos (7a) states that ‘Even the blessing of a simple man should not be light in one’s eyes’… a kal v’chomer (all the more so) your blessing Rabbi.”
The Rogatchover answered his friend “Why wait for me to give her the blessing with the aid of a kal v’chomer? You can do it even without a kal v’chomer!”
Quoted by Rabbi Isser Frankel, Yechidei Segulah, Tel Aviv, 1956, P.103