How can I prove that a bartender put something in my drink to make me sick?

You could never prove it. It's doubtful that the bartender keeps laxatives to punish those who return a drink though. Don't let the silly movies and stereotypes fool you. People in the service industry are pretty vigilant about what the customer consumes. If not, it's their job at stake. Bartenders usually walk out the door with the most money (on a busy night they can make a manager's whole paycheck), so they are the least likely to be that disgruntled. In smaller establishments, bartenders are also the front-of-house manager on duty as well.

Unless you went to the Dr. and had a toxology report done on your blood or something, there really is no way to prove that the margarita was tainted. You yourself don't even know for sure that it was the margarita that made you sick. Just let it go and don't go back there again, or at least don't order the margarita next time.

it is not possible to prove unless u collect sample of the same sealed in front of witnesses for forensic laboratory investigation, i think so.

It would take approx 24-36 hours for you to get a stomach virus from something you ate. Frankly, you have no case. If I were the restaurant, I'd make you list everything you ate for the 48 hours prior, and start doing tests from there. You'll have to include everything you ate, drank...people you were around (maybe you caught a bug), anything you ingested. You'd have to have a full battery of tests to determine the cause (at best, this is tricky); ultimately the burden of proof is on you to prove that they deliberately put something in your drink. Short of video evidence, you have no case. My suggestion would be to avoid this place in the future, and vote with your wallet, as the saying goes.

You, like many consumers in a strongly "customer oriented" country, are acting paranoid. I don't think they put anything in your drink, because I also sometimes get diarrhea from alcohol (I usually drink canned drinks, not cocktails, so there's no possibility somebody would slip laxatives in my drinks or whatever). When someone brings you a product you don't like, you can ask politely to change it, not freak out. Nobody has anything personal with you. And I think it's inhuman to not tolerate a little fault, that can be fixed. The ones who serve you are people too and it's a hard job. Imagine what happens when everybody starts freaking out and insulting them. Show a bit of respect. They are humans. And if you show respect, you'll be treated with respect as well. P.S. I'm not flaming you, I'm telling you my point of view and what I find many people do wrong.

You have to submit a stool sample at the hospital. That's where the ER doctor sticks his finger up your.....and they swirl it around in a solution then look at it under a microscope to see what bacteria gave you the diarrhea.

YOU CAN'T BUT GET SOME DOCUMENTS FROM YOUR DOCTOR, HE WILL BE ABLE TO TELL YOU WHAT YOU WHERE POISIONED WITH. QUESTION? WHAT DID YOU SAY TO BARTENDER TO MAKE HIM PUT SOMETHIN IN YOUR DRINK?