When thinking about telling a casual sexual partner about your HIV it's worth thinking about why you want to tell them.
The reasons you have for telling (or not telling) may depend upon the kind of relationship you want to have. For example, do you plan to see the person just once or are you hoping for a longer relationship? It may also depend upon the kind of sex you want to have. If the risk of passing on HIV will be very low, some people see no reason to disclose their HIV status. Others tell partners to make it easier to make informed decisions together about sex.
If you have just met someone, you might not feel that you know enough about them to anticipate their reaction. You might meet the person somewhere like a bar or party, where it feels out of place to talk about HIV. Some people prefer to talk about their HIV status in a more neutral environment, at a later date or wait until they have got to know the person better. Other people drop HIV into the conversation very early on, in a casual and matter-of-fact way, so that if the other person cannot accept it, no time is lost.