Weed Smoking Granny -- Viral Video Sesh Was Fun ... But I'M DONE Taking Bong Rips!

The video of 3 grannys getting stoned for the first time is blazing up the Internet ... but sorry pot enthusiasts -- one of the women in the video says she'll NEVER GET HIGH AGAIN!

Dorothea -- the most timid granny in the video -- says she won't try wacky tobacky again because she didn't like the way it made her totally lose control.

However, the Internet star tells us she now understands why there's a big fight to legalize it -- and she hopes it's decriminalized ... adding, "I don't understand what the big deal is about being high on marijuana."

Not surprising ... the director of the video says Paula (granny on the left) told producers she was down to smoke again after they were done toking up.

Bet she'll make awesome Christmas cookies this year.