low key fuck boy
A boy who you wouldn't suspect to be a fuck boy as they do not fit the stereotype. However they then surprise you by being a fuck boy, hence the 'low key' as they are unsuspected and on the down low but still turn out to be a waste of your time
"Omg Becky he didnt even look like a fuckboy"
"Ikr he's a low key fuck boy"
"Ikr he's a low key fuck boy"