Yes, it is possible.. But having a mutual agreement with the girl is very important. A girl can kiss a guy even if they are not yet in a relationship due to the fact that the girl really "likes" the guy or she has this "special" feeling for him. I've kissed girls that were not my GF and they allowed me to kiss them because they liked me or have this "special" feeling for me. I think it is called "Mutual Understanding." A "stolen kiss" could get you in trouble, and i mean trouble. DO NOT EVER DO THAT.