帅帅

Reduplication of single-syllable adjectives (AA pattern) softens and informalizes them. 帅 ('handsome') alone is a flat statement; 帅帅的 ('a touch handsome / cool-looking') is conversational and warm. Same pattern in 美美的 (měiměi de, 'pretty in a soft way') and 乖乖的 (guāiguāi de, 'sweetly well-behaved').

Casual, often spoken or used on social media. As a name, doubling characters (XX) is the standard pattern for Chinese pet/baby nicknames: 乐乐 (Lèlè), 萌萌 (Méngméng), 帅帅 (Shuàishuài).