The KISS rocker got a rise on Twitter New Year's Day by sharing his weird eating habit, with reactions ranging from bewilderment and disgust to admiration and relief ... the relief coming from the fact he wasn't trending because he died.

Turns out, Gene's been doing this for decades, and we're told he thinks it's a smart way to keep his milk icy cold. We're told he also adds ice cubes to hot foods -- like soup and ramen -- to cool 'em down. Genius.

His son, Nick, replied to his tweet -- which also strangely shows a bowl of Oreo O's and shredded wheat cereal mixed together -- saying he's been watching his dad do this for 30 years and adding ... "This is my life."

We're told Nick and Gene's daughter, Sophie, have always given him a hard time for his ice cube ways ... and Sophie's the one who encouraged him to tweet about it to see what everyone thinks.

Consensus -- yeah, it's weird man. However, some people accepted it and even offered tips to improve the practice ... like using milk ice cubes instead of regular ones so it keeps the milk cold but doesn't water it down.