This bloke goes into see his doctor and says, ‘Every time I see a lorry, I get an erection.’ The doc laughs and says, ‘Impossible.’ So the bloke stands up and walks over to the window and, after a lorry passes by, he pulls his trousers down to reveal a huge hard-on. The doctor says, ‘This defies medical science, but give me a sample of blood, then come back in three weeks and I’ll have a result.’ Three weeks pass by and the bloke returns to the doctor. On entering his office, the doctor says, ‘Sit down, I have some bad news for you.’ The bloke slumps into a chair and says, ‘What is it, Doc?’ The doctor explains, ....
‘You’re HGV positive.’
‘You’re HGV positive.’