A petard is an explosive device...

Boyfriend: *playing minecraft, and blows himself up, launching him into the air* AHAHAHAHAHAHAHAHAHA! I WAS JUST HOISTED BY MY OWN PETARD!!!!

The carrion birds and maggots...

Me: *playing Minecraft* Woah! Where did that zombie come from?!
Boyfriend: Well when a mommy and a daddy zombie love each other very much, they kill a child. And that doesn't grow up...

I actually meant that his mom was a creeper...

Me: *looking at Soul Sand* Yeah you're right, it has little creeper faces in it... like your mom.
Boyfriend: More like YOUR mom's vagina! They're wandering around in there going 'We can't do any more damage than has already been done! It's ALL bedrock in here.'

Ooooh, the puns...

Me: *playing Minecraft* I hear sheep... What the hell are sheep doing underground?
Boyfriend: I dunno, maybe they're deep sheep.
Boyfriend's brother: Related to Deep Crows, but more sheepy... sheepish...

When Minecraft meets my mom...

Me: You can build a portal to hell... you know, in case you want to visit my mother.
Boyfriend: Nah, your mother lives in Florida, which is SIMILAR, but not QUITE it.

Ah Minecraft... what?

Boyfriend: You never know! He could run off and tell the other sheep something, and then BAM! Creepers in my ceiling!
Me: So... you're saying Creepers and sheep are working together?
Boyfriend: Hey, both Creepers AND sheep are tricky!