Pigeon English/slang (of Norfolk origin perhaps?) for a negative. B'aint can be used to substitute many words such as "aint, won't, shan't, can't, don't, not" etc
If a girl is willing to be with you regardless of whether or not you spend money on her then it's ok to buy her gifts and not be seen as a trick... because you've already got her. It's only tricking if you don't have her yet and you're using the gifts to try and establish a relationship.
Now that I have money, I decided to spend a couple thousand dollars on my girl who's been with me since we were broke together and going halves on a shake at McDonalds, cause hey... it aint trickin if you got it.
John: "yo where you been i've been hitting you up all day i told u last night i needed you to take me up to the hospital to see my mom"
Mike: "i aint feel like leaving my house, i had this banging shawty over"
John: "niggas aint real"
said person isn't a "wuss" or is badass in some way. This can refer particularly to an instance in which someone is drinking, smoking, or doing something extreme.
Tom: "I bet you cant drink another shot" -offering another shot of vodka
Jim: "Daddy aint no bitch" -takes shot without puking