'I WUS BEING SARCASTIC!'

Unless you make it incredibly fucking obvious that you're being sarcastic in your comments...It doesn't turn up really well in text. It's understood much better through your tone of voice.

When I want to convey sarcasm, I use "!!1!!" at the end of my sentences. Or type in all CAPS. Or use the word "totally." Or make it sound so fucking stupid and use such fucking stupid logic, then there's a 99.99% chance that I'm obviously using sarcasm. My villain happens to be incredibly good at this.
_{Although, I have said something stupid and meant it...and didn't realize it was stupid until someone pointed it out to me. But I rarely do that. Usually I catch myself first when I proofread my comments.}

And using "I was being sarcastic" or "I was just joking" as an excuse for your blatant stupidity or for being a dickhead is just pathetic. If you made a mistake, just admit it. I'll respect you a bit more that way.