Do you often have a clown or jokester in your training sessions? According to the Urban Dictionary, a jokester is someone who loves a good laugh and never knows when to stop making jokes, although they are not always appropriate.
Perhaps the German translation would be a “Spassvogel”. According to the Deutsche Welle, a “Spassvogel” busies himself (or herself?) entertaining others. That was the court jester’s job in times gone by (link to: YouTube).