They always stress the fact that you have to leave by the day your visa expires. Even one day after and you could be in serious trouble. Of course, I've also had plenty of friends who've over stayed their visas by quite a bit and had no problems. So basically, it's all hit or miss, but when push comes to shove, you're not really allowed to.
Even though my visa expired on July 6, but I was determined to hold on to Europe till the bitter end (I didn't move home until 3 days before the semester began), my plan was to escape to Shahida in Scotland then return to Germany as a "tourist." The plan was to fly straight from Italy to Edinburgh on what I dubbed "deportation day" (no really, it was labeled in my calendar). Not returning completely home after a visa expires, though an accepted method, is still frowned upon. However, when I saw that flights the day after deportation day were about 30€ cheaper, I decided one day couldn't hurt - especially not leaving from Italy, they're really lax people, right?
What I didn't take into consideration was that I'd have to make it through 2 airports on the hopes that no one noticed/cared, as I had a layover in Mallorca. I figured they'd be just as relaxed as the Italians, being a nice vacation Island and all... also, my visa was all in German, and even though dates are in numbers, I was hoping coming across words like "Aufenthaltstitel" and "Aufenthaltserlaubnis" would scare them away from really checking.
Things I didn't take into consideration: when you fly Ryan Air, regardless of the fact that you're traveling within the EU (where they don't normally check passports), if you're not an EU citizen, you have to have your passport checked. Also, German words don't scare the people of Mallorca as that is the main travel destination for vacationing Germans. So much so that it's often referred to as the 17th German state.
So when I arrived in Mallorca with 2 hours less than intended because of a last minute rescheduling (thanks, Ryan Air), I was already flustered about missing my next flight to Edinburgh. So I ran to passport check, and that's where the shit hit the fan.
It was one of those situations when they asked me if I was in the EU as a resident, where I didn't know if a simple "no" would be a quick get away or a sure fire ticket to trouble. I'm still not entirely convinced this was the right decision, but having never been asked that question before at the Ryan Air passport check, I panicked and opted for honesty - "Yes, the visa's in the back" - Hoping they wouldn't really look at the date, or figure that it was just one day so who cares. But when I saw her start counting the days on her fingers and I immediately knew I had picked the wrong answer.
"This expired yesterday." Not even a question. 3 words. And then the worst case scenarios started flashing before my eyes:
Calling Shahida from the US telling her I had been redirected from Edinburgh because of an over-stayed visa
Calling my mom from the Atlanta airport. Surprise!
Having to pay exorbitant fees.
Being black listed by the EU from ever returning.
Something involving a plot very likely to appear on Locked Up Abroad
At this point, I decided honesty had failed me and started going for anything that sounded good "I'm flying straight back to the US from Edinburgh! I got a connecting flight from there because it was cheaper! I'm going to miss my flight (which was kind of true)." Whatever conversation occurred between us next is all a blur by this point, the next thing I really remember: she discusses the situation in Spanish with her coworker, stamps my ticket as being checked, and without another word sends me on my way.
For all I know, she stamped my ticket with "detain this person upon arrival," but nonetheless I ran to my gate with an overwhelming sense of relief. Now I just had to make it through the real passport control in Mallorca, arrival passport check in Scotland, leaving Scotland and arriving in Germany.
And I did make it, never to be almost detained for breaking international law again.