My first slide in a lesson today (I refuse to call it a starter, I'm a teacher not a waiter) said.... A neutron went into a bar and asked "how much for a drink" The barman said... The students had to write the punchline, discuss why the joke worked and make up their own jokes relating to the atom while I did the register (lower set KS4). Punchline btw... ...for you sir, no charge. I think this is a genuine contender for cheesiest teacher joke used in lessons. I re-use it most years, as I'm sure many other science teachers do. Anyone got more groan-worthy efforts?