another 'trick' is to poke the guy next to you and press the transmit button so he screams like a girl... heard it done on another watch.
but generally, its the person/people sitting at the sectors/positions next to that are having a laugh about something and you just get the giggles.
its nothing personal, and it goes both ways. every now and then i hear a pilot sniggering, i guess something amusing is occuring in the flight deck.
we are human, it happens and its nice to know that when we talk to eachother we are only human. its the complete grumpy sods i cant stand......