I seen is in no way, shape or form acceptable. It's grammatically incorrect, and is a major pet peeve of mine.
Saying "I seen" sounds like you are missing the helping verb (have), which you are. "I have seen" is the present perfect expression, while "I had seen" is the past perfect.
I think this may help:
Use SAW ONLY when you are speaking or writing in the PAST TENSE and when HAS, HAVE, or HAD is NOT a part of the verb.
I'm guessing E will explain it better.
I ain't thirsty. There's plenty of fish in the sea, but I don't want all of them, can I have some standards? Or do we just have to settle, for someone's who meh and will do.