Hi Kseniia, There's a couple of bits of background knowledge needed here. "Oregon Trail" was a popular computer game back in the 1980s or 1990s, where players could play as travellers on the Oregon Trail (a route that pioneers travelling to Oregon in the western USA took back in the 1800s). Lots of people died, usually of dysentery, which is basically very bad diarrhoea. The word "diss" is slang for insult. Terry, of course, is a name. In this case, dissin' Terry (insulting Terry) = dysentery (deadly diarrhoea). Nice joke, though!

Dysentery :)

Well, this is a terrible joke and I don't like it much, but as an English teacher I accept the challenge! To "diss" someone in U.S. slang is to insult them. So. dissing (dissin') Terry is insulting Terry, and "Dysentery" is a gastrointestinal disease, that can be fatal. There is also the verb "to disinter" but that doesn't make much sense here even if it relates to death. One more comment, Terry is short for Terrence and is a man's name, Terri is the female name. That's it, I would now really advise you to forget this awful joke!