Start Small
If the conversation is flowing naturally and there's mutual laughter, you can test with a mildly playful line. Think "are you always this fun?" before jumping to something spicy.
Watch Their Responses
Do they match your energy? If you flirt and they respond with equal or greater energy, you have consent to escalate. If they deflect or change the subject, stay where you are.
The Step-Ladder
Level 1: Compliment. Level 2: Playful tease. Level 3: Mild innuendo. Level 4: Dirty pickup line. Level 5: Direct expression of interest. Each level is a test. If they engage positively, climb one rung.
The Golden Rule
Never skip from Level 1 to Level 5. The people who fail at dirty pickup lines are usually the ones who go from "hello" to "let's go home together" in two messages. Build rapport first.