i heard that i should not run after a meal coz of appendicitis...
If someone says something like this, they should back up their claims with scientific studies. If they can't, they're either lying (this is most often the case if they are also selling something), or at best repeating a myth they once heard. Trusting their advice "out of precaution" may sound reasonable, but if you follow every piece of advice strangers on the Internet give you "out of precaution", you'll pretty soon end up not being able to do anything.
Having said that, there are many good reasons not exercise directly after eating. You'll likely be a bit sluggish, as your body is busy processing the food. It also happens at powerlifting competitions (and I assume, in gyms outside of competitions) that people vomit when doing heavy lifts (especially deadlifts), which sometimes is attributed to eating and/or drinking too much too close before your lift. (Nope, no citation for this, but my own empirical data say that a full stomach and high intra-abdominal pressure is not a great combination.)
But no, there doesn't seem to be any reasons to be concerned for physiological safety. (Vomiting on a roid-rage kind of guy at the gym may be very bad for your personal safety, though.)