Never been caught masterbating BUT many times with my ex girlfriend.
1) Had a bunk bed without the bottom bunk (sorry don't know the proper name for these.) and we were going at it too hard and wound up bumping the desk bellow and knocking over a fishtank, my dad rushed in to find a nude 15 year old me trying to mod it up quickly with my pants (which weren't on.). (I'm 19 now lol.)
2) Parents actually came home once while I was banging my ex on the counter top, we thought we would hear the door, but well in the heat of the moment we didn't. Got one hell of a lecture for that shit, and had to scrub the counter for hours before my step mom shut the f*** up about it. My dad found it amusing though I could tell. (was still 15 that time.)
3) Didn't get walked in on, but my ex and I were doing our thing on the kitchen table this time and it broke. I probably could have come up with some stupid story or another, but my ex's tush was on resting right where the crack for the insert was when it broke and it gashed her when she fell on it and it opened. Had to get her to the hospital and they called her parents, wasn't pretty to be honest. (Was 16 that time.)
4) Back in 07 when I was still leading a clan in rs, I accidentally left teamspeak on with the mic on (haven't used ts in a while so I don't remember what the service is called, but you can set it to stay on without pushing the button.) We had just had a clan war so it was stuck on. Needless to say it was one of the funniest moments of my 17 year old life with my ex, finished her off to turn on my speakers and hear a bunch of twelve year olds going "OH THANA OH OH OH THANA!" (yes my girlfriends call me Thanatos, it's far more than an internet handle.) and one of them even recorded it. 45 minutes long, funny part was at first they thought I was watching porn XD.
NOW FOR WITH MY CURRENT GIRLFRIEND!
5) Last year (18 at the time (STILL 07)) first time my girlfriend and I had sex week after I broke up with my ex (technically week before. But I'd been trying to break up with her for months so lets not go there and pretend it was the week after. Everyone I knew thought I'd already broke up with her anyways lol. NO i'm not proud I cheated, but at the same time NO i don't give a fuck cause she was a dumb irritating cunt.) My rents were supposed to be gone for a month and came back 4 days early in the middle of the night (THE first night me and my girlfriend hooked up too.) I thought someone was breaking in, my current girlfriend was putting on her bra and trying to get dressed without me seeing while I marched nonchalontly out into the living room in nothing wielding my Katana, needless to say that was a rather awkward conversation explaining why there was A) a woman in my bed and B) why it wasn't Emilie now my Dad calls when they're close to being home (moving out in the summer though but at least I'll have had 2 years of privacy

).
6) THE BEST TIME I EVER got caught, was about 2 weeks after number 5) we were in my car at the park (since going back to my place was out of the question for a while

.) and public security caught us. The guy was funny as hell though, he WAITED till we were finished (Which was at least a good 15 minutes from when I saw and ignored the headlights entering the parks parking lot, after all if you're caught your caught, and if it's just some paserby, let em pass by. No point in stopping until you got to.) then when I open'd the door to let some air into the smug hot car and defog the windows the Lights and siren went. Was pretty funny, went out in nothing but my jeans, and the guy gave me a warning (would have loved a ticket would have been worth it just to frame it and put it on my wall XD.) was epic.
7) THE LAST time I got caught, was with my girl at the laundramat, it closes at 10PM in our friends apartment building, but she's friends with the super intendent so she has a key, and naturally we borrowed it to have some fun on the spin cycle. The owner of the building walked in on us (we NEVER expected it to happen since the owner is only there like once every two months and usually not at 10:30PM) wound up streaking getting back to my place before she could call the cops.
Yeah those are pretty much my list of times I've been caught doing the deed. THese aren't counting all the condom wrapers my rents have found in places they shouldnt have been (When I first got my dog last year he used to love taking them out of the trash and surprised my parents with a used condom last year while they were eating dinner, got in trouble for that one too.).
Anywho hope a few of you get some laughs out of this
Thanatos.