A compliment in dating is most effective when it functions as evidence of observation rather than an expression of approval - and timing is the primary variable that determines which one it reads as.
A genuine compliment about a girl's eyes is a specific, observational statement that acknowledges something she likely notices herself but rarely hears described with real attention.
A "What's up?" text from someone you're interested in is a low-effort opener that puts the conversational weight entirely on you - how you respond determines whether the exchange dies or develops into something real.
A Hinge dirty opener is a flirtatious, suggestive first message that uses the recipient's own profile prompt as its anchor point - making it feel personal, not pulled from a list.