Literally, “stupid hair” in japanese. A single (usually short and fat) lock of hair that sticks out of an anime character’s head. The character is usually stupid in some way, but there are enough exceptions that this isn’t a rule. Example characters include Himeko and Me-tan. To be differentiated from antenna hair, which is two or more thin locks of hair as opposed to only one.
Rebecca grabs a hold of Himeko's ahoge and pulls it out.