Once the victim of your joke gets over their initial excitement of believing they just won $20,000+, they may turn the ticket over and read the fine print to see where to take the ticket and claim their money. They will then notice the ticket to be redeemable only at places like the North Pole or by the Tooth Fairy, and they will realize (hopefully) that the ticket is fake and they didn't really win diddly squat. Or they may take it directly to a gas station without reading the fine print, at which time the clerk will inform them that they need to contact Santa Claus or the Tooth Fairy to cash in the ticket.
Scenario 1: The Obvious
Offer someone you know a ticket as a "friendly gesture." Maybe buy some real lottery tickets for yourself and other people who are present to make it more believable. Everybody scratches their ticket, secretly watching the mark with the fake ticket, and everybody tries to contain their laughter as the mark reacts to the false belief that he/she just won big bucks! Then watch the grin melt off their face like water off a windshield when they figure out it's a fake!
Scenario 2: Thief Payback
Maybe you work or live with someone who you suspect steals from other people. In this case, you can "accidentally misplace" the fake lottery ticket where you know the thief will find it, stick it in their pocket, and claim they never found it. They may or may not come back later and get mad at you for tricking them into stealing a fake lottery ticket. HAHA!
Scenario 3: Shameless Entertainment
This is the one that you can do over and over again. When you go to someplace like a bar or a fast food restaurant, leave a fake ticket somewhere it will be noticed - like on a table or in the middle of the floor. Then sit down and relax, keeping half an eye on the "ticket" until someone picks it up and thinks they lucked into finding a scratch off that someone dropped or forgot. Laugh as they scratch off the ticket and rejoice, then laugh more when they discover they've been duped!
Other Suggestions:
Leave it as a tip for bad service. Drop it in a rude bartender's tip jar. Leave one on your boss's desk. Scratch one off yourself, make other people think you just won $20,000+, and let them all brown nose you for a while so that you'll share your new-found wealth.