Why do people find me an easy target to pick on?

i am a very nice person. i am also very smart and funny. but unfortunately,i am very gullible i believe almost EVERYTHING! i talk a lot too. i am also very very very short for my grade/age. i am 4 foot 10 inches and in, well, 10th grade! people say to ignore them, but i have some anger issues and i have a hard time ignoring people. (i got picked on all my life) and i kinda punched someone the day b4 xmas break. . .it happened to b a guy in 8th grade. (he was obviously taller than me. . .doesn't take much) lol