Have you ever been stopped at a border crossing, airport immigration, or port immigration and had your luggage/car searched?

No, but this year, when we came back from Michigan, our bags were searched because we had maple syrup in them!  We had wrapped them up all nicely in bubble wrap, and the people who search the bags (I forgot what they're called!) didn't wrap them up properly!  Fortunately, the maple syrup survived the long plane trips from Chicago to Brisbane, but I found it funny imaging these guys looking through our bags for drugs just to find maple syrup!

At a ground border crossing, I had to either chug back a half-drunk can of soda or surrender it.

~ seriously ~

I drank it, and was allowed to cross the border.

They made us open our trunk coming back from Mexico. And Coming back from Germany they asked if I was bringing back anything that was left with someone else at any part of my trip. My husband had taken in our video camera in to be repaired. They wanted to know the name of the business that had done that. I didn't know so they had to go get my husband to answer the question. (He was not flying back with me. He was in the Army and I had to get back to school.)

Nope, haven't been on a plane for many years.

Sure, quite often when going to any of the islands. I must look just like Mr. Random.

When I was a child, my aunt & uncle took us on a shopping spree in Tijuana, Mexico, where my uncle decided to purchase two miniature parrots.  They started crawling up my aunt's leg at the border inspection point, but we got through okay.  I'll never forget that day :)

At the airport in Puerto Vallarta there is a button you hit, and it turns red or green - red you get searched.  I was travelling with my ex wife and her family, he sister got a red light and gets searched - in her luggage she had a zip lock bag full of tide, (white powder). When they saw it we all get flagged for being with her, and got searched, and had the dogs come over and sniff our bags.  At the time it was not funny but later we all laughed about it over some drinks.

Repeatedly.

At Dover, having just arrived back from an exhibition in Frankfurt. There were two of us, a bit scruffy (we were in "roadie mode") the customs people practically dismantled my car - we were "clean". Likewise, 3 years ago, returning from Amsterdam. Used sometimes to get bounced at LAX, usually by a grinning 20-something in plain clothes. I once had to empty out my case on the floor there, for the guy concerned to eventually say "Nahh, you don't look the type." Scariest place is Saudi Arabia, where there is a warning that "The penalty for drug smuggling or drug possession is death by beheading." I always kept my luggage close to me when travelling there. Nastiest place is Lagos, Nigeria, where your luggage is always searched, several times on leaving, as various officers of various governmental organisations look for different things. It normally cost around £50 in bribes to get through there, even when you had nothing to hide. Heaven knows what it would cost if you WERE trying to smuggle something in, or out.