What is Laughing Gas?
1.
Nitrous oxide. Can be bought over the internet for 'culinary purposes'. A cheap drug that makes everything funnier, usually taken in a balloon so you get oxygen as well and don't die.
Mike: Dude do you wanna buy me some laughing gas?
Brett: Shit man i'm skint you get it.
See
2.
The result of laughing so hard you fart.
(Someone tells an awesome joke)
(Someone laughs & farts as a result)
"Dude, what the heck was that?"
"Aw, sorry man, it was laughing gas."
See