Actually, I love explaining my anime hobby to 
people.  Its very strange, but I find that all of 
my hobbies become very addictive to my friends as 
well.  Elfquest?  All my friends now read it.  
Star Wars?  Fancy that, I'm no longer the only 
one who makes lewd jokes about storm trooper sex 
slaves.  Pro Wrestling?  We got together and had 
parties on monday nights and spend the whole time 
making lewd comments about the men running around 
in spandex and the extremely gay positions some 
of the wrestlers put each other in.  Anime?  All 
my friends like that now too... it starts off 
insidiously... I just slip them a couple of 
episodes of a really funny series.. then I get 
them into the more plot-oriented series....and 
BAM! they're hooked.  I find it is much more 
effective to SHOW rather than tell people about 
what you're into ^_^

As for the disbelievers, I ALWAYS keep some 
hentai on hand.  You really wouldn't believe how 
handy that stuff is.  Nothing creeps out unwanted 
guests like tentacles.  Nothing freaks out people 
you lure into your room in 'altered states of 
consciousness' like tentacles.  And you can 
always tell them it was a disney movie 
afterwards.  Or ask them how they like the 
uncensored version of pokemon... whatever fits.