You should always tip something. If the service was terrible, tip 5%. The waiter will know you weren't happy.
The only people who don't tip are assholes and they better hope they don't frequent an establishment with their no tipping punk ass.
A play would have to be pretty damn terrible to justify not clapping at all. Like, not only was just crap, the performers were not even trying.
"Family Guy jumped the shark when i stopped getting high every time i watched it. " - Alex