A phrase to be repeated in any situation where there is something that you know you should pay for in some way, but you are not totally obliged too at that point in time, so instead you use the object/service for free.
Reasons for this should be down to the fact that you can't afford the object/service in question, thus making this phrase popular among students.
The phrase is coined from an observation of the Munich public transport system. The whole system relies on the system of trust, as conductors are few and far between. You should pay for a ticket, but it is easy too spend a week there, use the trams daily and not pay for one single ticket.
'This free drinks taster stand wishes that you give a donation'