The actual act of sexual intercourse, man-to-woman; woman-to-man. When I was young (many eons ago) they had the 'base' system:

1st base: kissing and maybe some 'under the sweater' action
2nd base: french kissing and fondling
3rd base: naked bodies rubbing together, but NO penetration
4th base or home run: sexual intercourse

It got stupid to say 4th base and saying home run during baseball season could be confusing. So the act bacame The Big Nasty.
Susie: Did Johnnie feel you up last night, Nancy?
Nancy: No Suze, we went all the way. Enjoyed The Big Nasty, donchaknow.
by Shmouse May 23, 2005
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Anal-oral contact, also referred to as anal-oral sex, rimming, or anilingus (from anus and lingua), is a form of oral sex involving contact between the anus or perineum of one person and the mouth of another. AKA - The defined art of butthole pleasures.
Angie: "That corn was really good."
The Big Nasty: "Boy, I would suck a fart out of her ass."
by The Big Nasty / L-Money April 12, 2009
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A process that used to be used back in the day by call center agents supporting cable modems. It was a long, multi-step average handle time killer that included ripping out Windows' TCP/IP components, removing and re-installing network drivers, deleting the related entries from the registry, deleting some Windows system files that were frequently corrupted, restoring the system files, rebooting a few times, getting up and doing the chicken dance on your desk, calling the Mentor Line a few dozen times and guzzling lots of coffee. Always done as a last resort, usually at the recommendation of a mentor.
John tried ripping the stack and the nic, but that didn't work so he just did The Big Nasty and that got her back online.
by Spirit Bear October 28, 2004
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Nickname for the amphibious assault ship USS Nassau (LHA-4)
The Big Nasty is always underway.
by moosee81 September 10, 2011
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Big Nasty is a badass motherfucker who spits game at every female and whips out his piece at any given moment . A Big Nasty can sometime be mistaken for a Big Chocolate Nasty in which The Big Nasty can Transform Into .
Guy 1 - Damn I wish I could spit game
Guy 2 - You my man need to meet The Big Nasty
by BadAss M'Fucker October 15, 2012
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A large woman who doesn't bathe, has a uniroll, and has a yeast infection from the crack of her ass up through her vigina following upward to and around her uniroll. That is the big nasty.
I don't think anyone would want an example.
by Thomas November 4, 2003
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Any large person who refuses to engage in daily personal hygiene, often smelling of rancid garbage and/or rotten cheeseburgers with onions on a hot day. Also the same person who refuses to courtesy flush who may have had a gastro sleeve whose stool is unbearable to the point of choking and/or vomiting.
Oh oh, get the spray out....here comes Big Nasty!
by Unc Vinny September 27, 2019
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