Johannsen attended Iowa State University in the early 1980s, originally majoring in veterinary medicine, and then later changing to chemical engineering. He left after three years in college and relocated to San Francisco, California in order to pursue a career in comedy. Johannsen made his debut at Cobbs Comedy Club in San Francisco, and by 1986 had won the 11th Annual San Francisco International Comedy Competition.
During the 1990s, Johannsen starred in his own HBO Comedy Special, This'll Take About an Hour, which was listed as one of the Ten Best Television Shows by People Magazine in 1992. In 1994, he was nominated as "Best Male Stand-Up Comedian" for the 1994 American Comedy Awards.
In 2010, Johannsen starred in his second Comedy Special titled I Love You, which aired on Showtime and was directed and produced by The Aristocrats editor Emery Emery.
Johannsen is a favorite of David Letterman and has appeared over 40 stand-up performances on The Late Show with David Letterman.