How Much to Tip at Supercuts?

A couple of days ago, I went to Supercuts to have a haircut.  As usual, I got a nice haircut from Nicole who has known me for over 7 years now.  I always ask for her every time because she knows how I like to style my hair and she does a great job too.  The haircut costs $15.95.  I always tip $5.

Now, I never gave a second thought about it because I always knew that I was tipping a little above normal.  I knew Nicole and I always tip people I know more generously than others I don't know.  However, as a GOLD STANDARD, my rule of thumb for tipping is this - 20% for good service, 15% for average or substandard service.  I don't punish anyone for bad service beyond this, because I think everyone has good and bad moments and in America, most people in the service industry who survive on tips need them. You wouldn't decide not to pay for your meal if it was lousy, would you?   Of course the restaurant might decide to comp you, but you don't get to decide whether to pay or not. 

Now, this time, at Supercuts, I was in for a surprise.  I saw two customers before me tip ridiculously low amounts - $1 in one instance and $2 in the other instance.  That is a tip from the 1990's!  I  was amazed to see the Supercuts employees smile and just accept the tips and they did not look at the tip with disgust.  One might say that reflects a well trained employee, but I felt sad for them.  A $1 tip for a haircut these days is never acceptable.  In fact, it is ridiculuous.

20% of $15.95 is $3.20, and a $3 tip would be decent.  Anything less had better have a good explanation such as "bad service"! If one cannot afford to tip decently, it is better to not tip at all.

What do you think?  How much do you think one should tip at Supercuts?