With the Nitty Gritty, you have to know what you are getting yourself into. I hadn't been here for my birthday for a couple years, and my last birthday reminded me why I loved the place so much.
Obviously this is a great place to go on your birthday. Free beer or soda or (this was news to me) a couple low cost cocktails all day! You get your mug (and a balloon or button if you are so inclined). Shots are varied and relatively inexpensive, and the food is solid. My personal favorites are the Gritty Burger and Fries (I can thank those fries for saving me from detox on my 21st Birthday!) and the boneless wings, which are HUGE thin chicken breast strips breaded and served in a choice of sauce.
The atmosphere is always fun, and really the only drawback is that it can be really crowded with somewhat slow service at times. I don't recommend it if you need to get in and out quick for a Badger Basketball or Hockey Game or for state High School tournaments.
But if you happen to have a day off on your birthday and can get a little loopy at lunch, this is a great spot.