In all seriousness, wouldn’t you find it fascinating to know whether an obscenely high proportion of computer mice or keyboards harbored semen traces? Like the cocaine on currency thing, but far more revealing.
Semen could be the least of your worries, depending on where exactly the mouse may have gotten shoved up.
Any search must begin with the dongle.
Probably not that bad…wouldn’t most of the semen contamination be on the user’s other hand?
Would that make it a mouse or a gerbil?
Offhand, I’d say that the odds may be good.
… But in that case, the goods are very, very, odd… 
Yes, actually, I would!
This is my line of thought.
Assumption 1. Every man who knows you can find porn on a computer has masturbated around their computer and gotten trace amounts of semen on the mouse.
Assumption 2. The majority of desktop installations, however, are at workplaces or universities, where masturbation is frowned upon. These mouses are clean.
Assumption 3. Women are not in the semen business, so, we can rule their computers out for semen deposits.
So all you need to know is figure out what proportion of desktop computers are owned by male individuals. Then that’s probably the odds that any one mouse in Goodwill will have been contaminated by man gravy. If you want to minimize your risk, purchase mouses that look like they’re from corporate setups, not consumer or gaming mouses.
There was a joke about this in The Dictator:
Nadal: I am a Mac genius.
General Aladeen: So what do you do?
Nadal: Mostly I clean semen out of laptops
Look, if you’re just not sure, there’s always Lysol Dual Action Wipes.
“Because, sometimes, Once is not enough…” 
A well thought out argument. As an aside, how common is it for women to mastaurbate to online content?
You learned this word, and wanted to find an excuse to use it, didn’t you?
I found the best source to answer this. 1/3 of porn consumers are women.
Wow saving up for four years? I’d have thought your OP would have been a lot bigger
I don’t know about you but all my favorite women are very much interested in semen deposits.
I wouldn’t be surprised at all if most computer mice have at least a trace of semen on them, same for even nastier stuff like fecal matter and urine. Not necessarily because people masturbate at their computer, but because you’ll have traces on your hands unless you clean up VERY well, and who hasn’t washed their hands afterwards?
After all, keyboards (and mice) are well known to be filthier than toilets. :eek:
So what if it’s brand new? How clean are the hands of the third world workers who put mice in their packaging? If we are going to be paranoid we may as well be properly paranoid.
Just look for this sign in the mouse department of your favorite secondhand store. And if you don’t see one, the manager will be happy to show you the health department report.
New ones are probably ok, third world workers don’t have time to masturbate.