To feel a girl or guys bare stomach. It's in between the "upstairs" and the "downstairs"
Man I went on the stairs insidies on Katey the other night. She loved it.
by Gangstuh D. Piddy September 3, 2011
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A bodily mutation where the penis slowly turns inside out, until it morphs into a useless sack of veiny skin

Causes include: being named John Smith, playing “Greenville” on Roblox, and listening to Don Toliver
Man, you remember that John Smith guy? I heard he got Insidious Retrogressive Genitalia Disorder!
by JohnSmithKiller2646 May 13, 2023
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A trash person that tries to get with a person that already is in a relationship. Probably also has some type of std given the name.
Person A: Where did you get your chlamydia from?
Person B: From Insidious Infection
by SuperTEAAAAAA August 22, 2021
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To cause harm over time. but also known as a syndicate created by 4 hot men.

as each of the hot men cause harm over time it makes sense.
hotman1: bruh lets be mean, but over time so we can cause long term issues within our friendship groups and cause havoc like the hotmen we are.
hotman2: u mean being insidious
by ssoonn December 18, 2021
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A destructive agent that can be living or non living; but it moves in a way that is highly un detectable with a malicious intent; With one who this agents intentions are set apon ("one"speaking exclusively on living and intelligent beings; Especially Humans) This "one" or "victim" becomes more vulnerable to defeat as the level of their pride, or lack of humility rises; Therefore insidousness is best detected with humility. Insidious is a word that doesnt, and shouldnt have an exact definition regarding the level of insidiousness; as insidiousness should always be assumed to be capable to adapt its insidiousness to no definitive level ceiling. Insidious is a word that really should serve as a warning that their are things that we have no chance of outsmarting or beating; and they dont want anything goood for us.
Why is it that the majority of mankind has a belief similar to one that states "Many will be decepted", but never have I heard in Church, as I am Christian a sermon or conversation in any depth on this subject. I can only see this as mass deception being something very real, and ever present... Were mankind to ever grasp the true length that insidiousness can go, then they would also know it doesnt have any point in which it cant go further: Mainly speaking in regard to mans limits... I just wonder, how much do people really opperate out of a decepted, and dumbed down thinking?
by W. J. Valentine August 1, 2021
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