Is there anything wrong with being feminine? No. There isn't. You have a right to be who you are and not be ashamed of it. But at the same time, as much as people are challenging your fundamental views of what is acceptable and unacceptable behaviour for a male, you're also challenging theirs... and that's always going to produce friction.
I think there has to be a balance. Mind your own business, do your own thing, but resist the urge to preach against stereotyping. If someone asks if you're gay, tell them that you can see where they might get that impression, but you're just a sensitive guy and confirm that you are straight. If they continue jibing you, calmly ask them why your sexual orientation is of such concern for them.
Easier said then done, I know. You can have the most biting remark ready but if you they smell an ounce of fear in you, your beliefs and behaviours, whether they're feminine, masculine, or anything else, are going to be ridiculed until you build up your confidence.
Personally, I don't think these people bother you because you demonstrate feminine behaviour; I think they bother you because they see you as an easy mark and the 'feminine' thing is easy to fixate on and ridicule. There are lots of people who have had brush with bullying, and the only thing that they have had in common is poor self-esteem and the inability to stand up for themselves.
I think you need to look into self-acceptance and some confidence building strategies rather than ponder the complexity of gender stereotyping. Be true to yourself, don't change for anyone... but be prepared to stand up for yourself. Once you do, I guarantee that the majority of them will leave you alone (I say majority, and not all, because some people really are incurable jackasses... everyone has at least two or three of them in their lives).
Be who you are and be okay with it.