I am jealous of him because I am dumb and not good at sports.　あってら、頭悪いちゅーのにで

I who am dumb and poor at sports.　うん、だが、ピリオドは入れない、これで文が完成していないからね＾＾

I being dumb and poor at sports.　MyselfをIと代えた方がいいと思うが

I to be dumb and poor at sports.　I to beはない文法だね

I, dumb and poor at sports.　これってなんか詩的で言えるんだけど、指摘だからこんな文だと・・・ね

それとも、日本語みたいに体言止め(A sentence that don't include a verb and last word of which is noun)は出来ないのかな?? できる・・・ので、以下の三つは没

I am the man who is dumb and poor at sports.　一応文法上ではあってるだが、かなり変に感じる英語・・・なんとなくｗ

I am the man being dumb and poor at sports.　これ、あってない・・・あの、なんと言うか？間接詩だったかな、Whoとか、そのやつらがManの後でいる。そして、あってもI am the man who being dumbの文になるから、日本語で直訳すると「頭悪かったりスポーツが下手だったりする自分」なんだから、変

I am the man to be dumb and poor at sports.　これも、変だが、文法上ではあってる。しかし、こんな文法は普通こうゆう文章で見るせいか「He is a man to be admired」やっぱり変な感じ・・・こうやってIs...To beはなんか「XXに値する」って感じで使わなくちゃ・・・なんないのかなｗ、前に言ったとおり文法は苦手だから、あくまでも自分の推測だが

Sorry, I'm writing this entry in Japanese. [Smoother alternatives: I'm sorry for writing this entry in Japanese. Please excuse my writing this entry in Japanese.]

I am envious of him because I am dumb and not good at sports. ["Jealous" is not wrong, but "envious" is more natural here.]

Whether or not the sentence is not a common phrase, the meaning of it may make sense. [Alternative: Whether or not this sentence would ordinarily/usually be said this way, it may make sense. Note: "The meaning of this sentence makes sense" would be redundant; you would say "This sentence makes sense" instead.]

Then, 『頭が悪く運動も出来ない自分』だけを書きたい場合はどうなる??下のように書けるのかな?? [Is this a complete sentence in 日本語, or did you mean to follow it by 彼にしっとしている in each case? The English translation of 頭が悪く運動も出来ない自分 will depend on whether this is the whole sentence, or is followed by "I am envious of him" or "I envy him" or "I envy his ability/abilities."]

I who am dumb and poor at sports, myself. I, who am dumb and poor at sports (myself), envy him. [The longer sentence is possible, but a bit awkward.]

Being dumb and poor at sports myself, I envy him. [This is natural, but "being" is not possible in the shorter sentence. Alternatives: Not being smart or good at sports myself, I envy him. Being neither smart nor good at sports myself, I envy him.]

I am dumb and poor at sports. [The phrase "to be" is not possible either for the short sentence or the longer sentence.]

Dumb and poor at sports as I am, I envy him. [This is only slightly awkward. The short sentence is not possible with this phrase.]

それとも、日本語みたいに体言止め(A sentence that don't include a verb and last word of which is noun)は出来ないのかな?? [In English, every sentence must contain a verb. If there is no verb, the phrase cannot be a complete sentence.]

I am a man who is dumb and poor at sports. [If you use "the" in this sentence, you are claiming to be the only man in the world with these attributes.]

I am the man being dumb and poor at sports. [I see no way of repairing this without using a clause introduced by "who."]

I am the man to be dumb and poor at sports. [This, too, cannot be repaired without using a clause introduced by "who." ]

「 adjective+I 」「adjective+you 」　とだけ書きたい場合はどうすればいいんだろ?? [ "<adjective> + me" and "<adjective> + you" are possible in incomplete sentences; "<adjective> + I" is not. Example: "Silly me! I forgot to bring my lunch box to work."]