Vocalizing in front of an [[electric fan]] (or similar device). Usually accompanied by text that's abnormally elongated. If there is text, but it's not elongated, then the subject probably isn't fan speaking. If there isn't any text in the image at all, use your best judgement; [[open mouth]], [[leaning forward]], [[closed eyes]], etc. are all good markers. 

Notably, Japanese children can be heard saying 「我々は宇宙人だ」, or "We are aliens", in front of a fan, owing to the alien-like voice distortion the fan produces.
ワレワレハウチュウジンダ ワレワレハウチュージンダ ワレワレハ宇宙人ダ ワレワレハウチュウジンデアル 我々は宇宙人だ