Next time you ask to borrow a friend’s iPhone, or decide to mess with his settings when he’s out of the room, remember this: That iPhone is probably filthy.

No, seriously – we’re talking about all sorts of fluids.

Electronics trade-in site Gazelle conducted a survey of iPhone users to mark its 5th birthday, coming up in a couple of weeks. And a couple of their results definitely make you think twice about touching any device that’s not your own.

That’s because 85% of iPhone users reported using their device in the bathroom. That’s even higher than another recent survey from January that pegged the figure at 77%. It appears that everyone really is using their throne time as office time, making calls, sending texts, browsing Facebook and checking email.

Even more surprising, 4% of respondents reported using their iPhones while having sex. The survey didn’t get any specifics – so it’s our best guess what they are doing on their devices during that time. Snapping a photo with Instagram, texting an ex, ordering a sandwich – who knows, really? The point is, between bathroom and bedroom antics, your buddy’s iPhone has most likely seen it all.

Although a small percentage of people are actually using their iPhones while engaged in recreational bedroom activities, an even larger proportion of those surveyed care more about their device than sex itself. A stunning 15% of respondents said they would give up sex instead of going a single weekend without their iPhone. Talk about brand loyalty.

While the bathroom and sexual stuff are the fun parts of the survey, some of the more interesting results discuss how consumers have become attached to their iPhones and what they want from future models:

Consumers want an iPhone with a larger screen. Nearly 40% of respondents report a bigger screen is the feature they would most like to see added to the next version of the iPhone. Apple has remained non-committal about whether the next version will feature a larger screen, but if the decision was left in the hands of consumers, we’d all need a little extra room in our pockets and purses.

Thanks to iPhone, consumers have been able to reduce the number of devices they own. Nearly 70% of survey respondents report waving goodbye to their iPod or mp3 player since purchasing an iPhone. Fifty-five percent have ditched their camera, and over 40% have gotten rid of their GPS unit since buying an iPhone.

Three years ago, I would bet you that the number of people admitting to poop-phoning would be much lower than today. Now, it’s somewhere around 80% in most surveys. I fully expect that trend to continue with the sex-phoning – as I’m sure that more than 4 out of 100 have fired up their device in the sack.