Saenai Ojisan to Oresama Yankee-kun

Subaru, a short-tempered young man, is walking one day when he casually saves a dull uncle. The uncle, two decades his senior, smiles and tells him he's a nice, good boy. For the first time in his life, Subaru is smitten! Even after they part, Subaru can't stop thinking about him... is this really happening?!

(Source: Seiunsha, translated)