Tunnel Brothers Share definition Flag Tunnel brothers are 2 men who have had a common female sex partner in their past. Gerald is currently digging out Muriel, who used to give it up to Asa. Gerald and Asa are now tunnel brothers. Tunnel Brothers by Straylight990 February 10, 2010 0 0 Get merch Get the Tunnel Brothers mug. Buy Now — $32.95 See more merch