One of my most memorable claymore incidents went like this:
On Mashtuur, the USMC held the Mosque, and I spawned as Sniper at Hotel, then trekked across the riverbed to slip around the side. On my journey, I realise that there's a US sniper on top of the house overlooking the bridge, so I decide to see if I can take him out, but no dice on getting a shot at him.
So, nip around the back of the house and through the gap in the fence. I go up the stairs really carefully, 'cause I figrue he's got to have it mined, and sure enough, just inside the door there's a claymore. BUT. He's positioned it really badly, it's kinda pointing the wrong way. I decide to take the risk, and make a diagonal jump through the doorway, and the mine ignores me.
So, I sneak up the rest of the way and get in behind the guy on the roof. He's nicely tucked away, and merrily sniping my teammates over at Hotel. So I pull out a claymore and put it right behind him, then I run off (parachuting off the roof, don't want to risk that mine-jump again). I realise of course that I should have just shot/stabbed him, but this seemed funnier. A few minutes later, I realise that that mine never went off.
I figured that he was just totally camping up there, and hadn't moved even the inch or so it takes to trigger the mine. So, I typed into the chat something like "Hey [insert snipers name here], don't move, I got you right in my sights!". Sure enough, the next thing that appeared was me picking up a claymore kill.
The guy went nuts, too. Kept insisting that there was no way I could have gotten a claymore behind him without hacking, 'cause he'd mined the entrance.
So remember kids, if you're going to play with explosives, make sure you don't do it wrong, or some bastard's going to sneak up behind you and blow your arsehole out through your ears.