...The gutter, most likely.
Given that you are using the internet I think I can assume that you are a human being. Human beings have what we often refer to as a sex drive or libido, which influences rational thought.
This driving mental force has its roots in our species early survival, and can be thought of "Mother Nature's" way of encouraging us to breed, and therefore remain a genetically competitive life form.
The problem is, we have evolved to a point where we no longer require these impulses to propagate. They certainly still play a role, but things like maternal instinct and the desire for ones legacy to "live on" are more than enough to convince us to breed, not to mention the physical feeling of sex purely as an act.
Do not confuse the physical sensation of sex with the sex drive/libido! A biologically mature human experiences these "reminders to mate" regardless of personal experience; You need not have had to have sex in the past to feel their irresistible tug. All chemically "normal" humans experience it, and it has a profound effect on our outlook and society.
Urges to mate tend to arise at times that can seem quite random to us, as our mental complexity and subconscious has long since enabled us to link sexual drives to anything at all- Any season, any mood, any occurrence can remind us to mate in this way.
Some research indicates that an average human being feels these urges many, many times in any given day, meaning that as you are reading this, there is a fairly high chance that, on some level, your mind is occupied with thoughts of copulation. Merely the act of reading this has inevitably caused you to think along these lines, at least for the time being.
In American society, being easily reminded of "dirty" or sexual acts by ordinary events and circumstances is colloquially referred to "having ones mind in the gutter".
So, in closing, I respond to your nonsensical question with a very rational and statistically accurate answer:
Your mind is in the gutter.