Hubby and I got the same T-shirt from his sister.
I wanted mine to look more like a girls, so I took my favorite t-shirt pattern and placed it on top of the shirt. I folded up the hem of the sleeve pattern and placed it on the hem of the sleeve. The shirt's length was perfect. I then cut all the new pieces out of the original shirt and sewed it back together.
No problem telling which shirt is mine and which one is his now.