Generally by the time the option comes up for you to flirt you're already knees deep in awkward land of heavy sexual innuendos and suggestions....at least this is how previous BioWare titles worked and I am not expecting this to be different.
I don't get what really bothers you. If you imply that romancing a Qunari is bestiality, then you don't know what bestiality is. Qunari horned beings in this fantasy world is a race, not a different species. The result of humans, elves or dwarves mating any of them might result in a viable pregnancy.
If your issue is the impending terrifying possibility of any of the characters that you are not interested in romancing would approach to you and make a casual flirty comment and you will call that "knee deep in awkward land of sexual innuendos and suggestions", then remember that you will always have the option to just ignore them, to avoid pressing the heart/flirty response, to press the dialog option that will change the topic. I don't know about your experience with this issue in the real world but if you get upset every time someone try to flirt with you and you find that person's behavior awkward and difficult to take, then you have a real problem and I would suggest you discuss it with a therapist.