This can be described as behaving romantically with someone you are sexually attracted to, either playfully or with serious intentions. While it is not a sin to be attracted to those of the other gender, how we respond to those attractions may lead us into sin for 'harmless' flirting rarely, if ever, actually

Is my conduct honourable?

is. The sin of lustful thoughts should be absolutely avoided (Prov 4:23, 6:25; Mt 5:28, 12:35). All interaction with those of the opposite sex must be wholesome and above reproach treating them as your father, mother, brother or sister with absolute purity and integrity (1 Tim 5:1,2). We should act in a way worthy of the Lord, being a good representative of His, displaying God-honouring qualities such as godliness, kindness and respect, not with inappropriate behaviour(Gal 5:22,23). Whatever we do should be for the glory of God (1 Cor 10:31).

See also: behaviour, dating, integrity, intention, lust, romance, seduction, soul ties, temptation.