Don't apologize for not tipping. Acknowledging that you suck is not the same as not sucking. Oh, and don't say "I'll get ya next time." We know all about you. I recently went to the airport and had to take a shuttle to the terminal. When I got there, the driver that had been very nice and accommodating, helped me get my bag out of the van and pointed me in the right direction. I reached in my pocket and then remembered I had changed pants just prior to leaving and my cash was in the other pairs pocket. I apologized and explained that I would get him next time. He looked at me like, "yeah right pal". I flew again a couple weeks after and saw the same guy helping someone else unload their bag, I ran up to him yelling, "excuse me, excuse me", he stopped and I gave him 5$ and said you may not remember me but..., He stopped me and said, "I remember, thanks a lot man". It felt good.