Since I have lived in or near Greensboro my entire life, I am very familiar with the area. Greensboro has a very rich history of dirty dive bars and I am here to list the very best for you.
The Bench Tavern
The Bench Tavern is located on Lawndale across from Target(2614 Lawndale Dr). It is members only and they are very strict about this but if you are really nice, you can usually get someone to sign you in. It is Greensboro's oldest bar and it has a dedicated following. They usually have good drink specials and provide wings or some other food on Sunday's during football for free. There is even a pool table in the back for all you ADD folks.
College Hill Sundries
College Hill is located on the corner of Mendenhall and Spring Garden (900 Spring Garden St.) This is a favorite of the college crowd given it's close proximity to UNCG. You can always get a reasonable priced beer here and the bartenders are top notch. There is a pool table and a Foosball table along with several video games to keep you entertained. This place has special dive status because when they try to clean it up, they lose business. That is just proof, that everyone likes a good, dirty bar. (dog friendly)
Westerwood is the coup de gras of Dives in Greensboro. Located at 508 Guilford Ave, it is definitely off the beaten path. They have a bar, a pool table, a Foosball table, a photo booth, a few video games, and a great little patio area for drinking, or jamming, or various other activities. They also have some of the best drink specials in Greensboro. If you are lucky enough to have Patty as your bartender when you visit, I promise you will be entertained. She is super high energy and just fun to be around. (Dog friendly)
You can view videos of jamming on the Westerwood patio here (RIP Mr. Benson):
All the bars on Walker St. There are 3 of them: Suds and Duds, Walker Street, & Wahoos. Be sure and check them out as well. They usually have great drink specials.
*Another place worth mentioning if you visit Greensboro:
This place is not a dive at all. They brew their own beer and it is awesome. Check them out. http://bigdraft.com/index2.html