What makes you decide and agree that a guy is Gay?

like makes u think someones gay or not?

his looks? well he didnt choose it!
if hes happy or not? (wtf lol)
his voice? he didn't make his voice like that!
the way he dresses? if yes, then what clothes do gay guys mostley wear...?

im talking about any guy...in general...what makes u think he's gay!?