The fire brigade
 

An hotel was burning down so the fire brigade rushed to the scene. When it was all over, before they satrted rolling up the hose pipes, the chief had a roll call. Two guys were missing so he dashed into the smouldering building to find them.
Eventually he found them in a room, naked in a bed together, sucking each other off.
"What the hell do you think you're doing?"
- "I'm giving him artificial respiration," one replied.
"Artificial respiration is mouth to mouth!"
- "I know. That's how it started."