Czechs can legally purchase and drink alcohol when they turn 18.
Almost all Czechs turn 18 while still in high school (senior year).
This of course means that graduation is celebrated with alcohol, even during the senior “prom”. In the Czech Republic, however, the “prom” is a huge official ballroom-esque event that is attended by suit-wearing and dress-wearing students, parents and teachers. The event does not take place in a decorated gym, but in a local building that is most suitable to host gala dances like this one. And yes, students who have already turned 18 do drink. A lot.
The “last bell ringing” is observed by seniors in May. It is the last “official” day of school before their study week after which they take their graduation exams. And the “last bell ringing” is celebrated in the streets. Students dress in funny costumes (“funny” means that male students dress up as nurses or prostitutes) and they collect money from pedestrians. This time, the money collected is of course used to purchase booze for “unofficial” party, where “drunk” is far from reality. Waaaaay too wasted would be more appropriate.
I live in downtown Brno (two-minute walk from the main square) and I see them all the time. It takes three weeks (not all schools have the study week at the same time). You meet one group, you give them money. You meet two or three and you start considering it, depending on how inventive their costumes are. But it does get annoying real fast, especially since it is more than obvious that the young people are going to buy vodka with the money I give them.
Sorry guys, I just gave my last change/coins to a group around the corner is the “excuse” I have prepared.