If we're only discussing gender related issues...
Well...
Some people might assume (as a male) the following apply to you:
1. You are capable of drinking massive amounts of alcohol.
2. You have a large dong.
Some people also have superficial attractions to foreigners because, well, they're foreign. Certain preconceived concepts about your.. uh.. sexual prowess could be a factor...
Then again, MOST Japanese people I know treat me like all people who know me. Whatever superficial conceptions you run into, they'll disappear once you step beyond the realm of casual acquaintance and into true friendship.