A garment (often knitted) worn over male genitalia to keep it warm. Sometimes used in cold climates, but also sometimes used by male dancers as a costume piece. Also known as a "willy warmer".
Bart was getting a chilly wily, riding his bike in the winter, so he pulled on his peter heater and it was all good.
When you take a really relieving early morning shit and glance down to see a perfectly sculpted replica of the peter you took in your heater the night before.
Hey babe, lats night was great! How was that Heater Re-Peter this morning? Did it have a little bend in it? Love you!