Pretty gay, downie, stupid af and has no brain cells at all. If you ever meet a Tim you have to get away from there as quick as you see him, he will suck your brain cells out of you because he's so empty in his head.
Random guy: Is that a kid with downsyndrome or is that Tim?
Random guy 2: Both.
Tim is usually a guy who likes to suck big dicks. He is also a very autistic person. Most Tims never experience somethings sexual with a women but most of them already have experience with there oncle at the age of 8.
A "Tim" is a collective noun which refers to Hello Internet podcast listeners. The name was originally coined by CGP Grey, co-host of Hello Internet in "H.I. #7: Sorry Language Teachers" at 52:40, referring to the fact that there could be a listener called Tim listening to the episode in an airplane.