Unfortunately for me though, 90% of the people I meet have no concept of what ace or asexual means, so I end up having to explain it in detail anyway, haha. Most of the time with strangers, I just avoid the topic all together. I'm not very eloquent in real life, especially if confronted about anything.
I work at an electronics store, and I cannot believe how many people (mostly older men) make some casual comment about my "future husband." They're usually in the form of compliments, or, alternatively, it's the "never get married" advice from someone who's just had a fight with their spouse (this comes from a lot of my married friends as well, even the ones that know I'm ace!). It always makes me very uncomfortable, and it's gotten very tiresome to realize exactly how many people just assume that everyone they meet is straight.
Yeah but to be fair, asexual is not a common thing. About 0.05% of everyone I've ever known is asexual, so it helps explain why most of society has no idea what it is.
When you explain it, all you have to say (without going into the specifics because I don't know your case) is, "I am not sexually/romantically attracted to anyone, period." (If that's your case).
Short and sweet and it stops people from saying that stuff.
But again I wish people would be more conscious of the different sexualities, but please do remember that a lot of people are hard headed and will say "oh you haven't met the right gal/guy that's why you don't like any of them. :(