Not all kisses in television can look realistic and perfect because there's lighting and camera angels to consider. As is always mentioned in interviews and commentaries, and what not; it's not even really like they're kissing the other person, because it's all about getting the light in exactly the right place and to be honest after several takes of one kissing scene, I can imagine they actors aren't going to be too bothered about how realistic it looks, because most of the time people barely notice. I will admit, I don't pay much attention to what making out or kissing in BtVS looks like, because I'm usually either too busy thinking how cute the couple is; or too busy wishing they'd break up already. However, I will agree some scenes are a little over the top, or occasionally not too realistic, but I don't think it's that bad.
