Stag do...

I was at my mate's stag night yesterday, when he and his brother handed me a glass full of yellow, lukewarm liquid.
"Drink it," they said, giggling. It was only when I smelt it that I realised the prank the b*st*rds were trying to pull.
"Drink it," they said, giggling. It was only when I smelt it that I realised the prank the b*st*rds were trying to pull.
Spoiler: