"I love your product." Just go up to any founder at a sub-Facebook or Google level when they aren't otherwise highly engaged/busy. Approach, but don't interrupt. Then, say it for real, with a quick example, "I used (your product) last week to (close a deal)." Love it.
It always works. At least it always works on me. Even just today at lunch.
Parents tend to be proud.
Sounds like rather awesome advice to me.