IF you know ohm's law, sub ohm "rules" et al, SMPL can be used safely. All the normal rules apply- with the additional concern of the 510 ...
PSA: quiz yourself. What batteries are you using? What's the amp draw if you build a 0.6 setup? An 0.4? What margin of error do you allow between that amp draw and the continuous (not pulse) rating of your battery? How sure are you you got all those right?
IF (& please only if) you passed the quiz, read on...
Start with a quick summary of everything everyone has said, and the why of it-- look at the protruding end of your atty. Any atty. The threads are negative, the pin is positive. Of course, the top of your battery is positive, so only positive must touch or you get a short. A "traditional" mech with a 510 pin of its own, handles this concern for you- a hybrid does not. You must use an atty with an adjustable, not spring-loaded, 510 pin. In practice, many can't actually be adjusted "down" enough for hybrid use without causing other problems e.g. loose posts in the build deck (which is in turn a bit more serious than just being hard to build on - a loose post means a loose connection and has potential of causing a short). If you choose to use the SMPL, I'd advise go to a B&M and hold some RDAs in your hand, fiddle with em, etc. You need at least a 1-2mm protrusion while maintaining solid build post connection, for safe hybrid use. Drop the cash to buy what you like there this one time. Reason being, internet shopping can be tough - even if you get a name from your store adventure and Google it, you may or may not get the same clone model as what you held...etc. Try online shopping again once you have one reliable "safe" atty to use.
Now...this is important. The black spots don't NECESSARILY mean you shorted. The black spots are carbon buildup which mean your battery arced. Some of this happens with normal use because as you push the button on your SMPL, your connection points physically approach the battery terminals, and when they are microscopically close but not perfectly touching, arcing occurs. (And arcing buildup, like any damage to your switch, messes further with that 'perfect' connection and causes exponentially more arcing.) Stay with me here cuz you gotta know all of this if you're gonna safely use any of it...
Hot button can be way more serious. If it instantly became super hot, yes you shorted, dispose of your battery any time this happens. If it simply heated up gradually in the course of normal use, however, here's another possible explanation. Let's go back to basic electricity - in any circuit, heat happens at the point it encounters resistance. The most heat happens where you have the most resistance. Obviously you want this point to be your coil, and you want the most difference that you can get between coil resistance vs any other resistance. Remember that your switch has internal resistance, as does your battery itself. (Heck, so does the tube, etc). In both situations, this internal resistance increases with use. (Battery decays with time & use, increasing internal resistance; your switch oxidizes, arcs causing that carbon buildup, gets dirty with skin oils et al, the list goes on...all of which increases your switch resistance.) If either of those internal resistance numbers is too close to (or heaven forbid, more than) the resistance of your atty, you've got trouble. In future, even a "minor" hot button means you should stop, clean, and rebuild higher.
So, if you're still with me through all this, here's what you do. Ditch your battery this time cuz you don't really know what exactly happened and IT ISNT WORTH YOUR LIFE if you're wrong. Break down your mod, your switch (all the way - even a u-clip/magnet can break down, and must to clean w/o causing more buildup than you have now - Google or ask here if need be). Clean ALL connection points including the threads on your tube with a mild abrasive... I like toothpaste. Rinse well. Soak in rubbing alcohol briefly just because it'll dry faster if you do. Set em out on a paper towel for at least an hour (unless you skipped the alcohol step, in which case dry em overnight). Put it back together and grab that new atty you played with before you bought, so you know the 510 comes out enough without any post spin. Build your atty to at least 0.4, I'd recommend you go higher. I say at least 0.4 because that's the lowest I've ever had work in a well-kept clone SMPL without issues. I started my dad on a 0.8 so he had margin of error as he learned, and I hope you'll start there too. Anyway... Put your new battery in and fire it up. If your button heats at all, check everything, then rebuild higher- check your ohms, increase em, check your 510 pin, check your switch and the bottom of your battery for arcing spots. IF you stay on top of it and can say you know you haven't ever come close to a hard short, then you can maintain that NEW battery (again, don't try this on your old one, as you may really have shorted that one) - by using a pencil eraser to take off those black spots from your battery & your switch.
I know it's been a long post, but this is all what we don't normally tell newbies because there is SO much you HAVE TO keep up with each part of. I'm not exactly comfortable saying it all here either, but it sounds like you're gonna use your SMPL no matter what everyone says, so I want you to at least do it safely. Be careful and come back as often as you need to for any questions.