This means that somebody was too loud during sex the night before.

'Microwave' refers to the coitus that was had.
Justine: Good morning, guys! How did you sleep?
Carla: Not very well.
Justine: why?
Carla: I heard you using the microwave last night..
Justine: Oh dear..

'You're just jealous because you heard HER using the microwave but you can't handle that heat!'
by #THE_QUEEN November 17, 2016
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friend: "Hey did you use the microwave last night"
other friend: "HELL YEAH I DID! "
by jsurfs November 26, 2016
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