1) person a:"I was hitting on this girl last night, but she has a boyfriend"
person b:"Oh, you're tight"
2) someone slips on ice and hits their head
3) someone lets out a nasty fart in public, and a really hot girl/guy looks at them weird
I have only heard this being used around my area. (Dorset, England) At school if a teacher has been mean to you given and made you do something (e.g. a detention) we say it's tight.