this ones seems pretty easy honestly.
The entps are always a little "shinier"??? they seem to pay attention to thier appearance and appear a bit stylish, if in an odd ackward way. Like they will match really nice sunglasses with really scrubby sneakers or flip flops, but they will put gel in their hair, so they kinds pull off the "Im so cool that I dont care i look odd" cool look. They also seem more relaxed but "watch" you to see what you are going to do next. They study you with a fairly intense focused Ti look. They can appear pretty easy going as well, and be very "friendly" pretty quickly. When talking they also look up to the left or right a lot.
Intjs tend to look more stuffy, more reserved. They look at you directly but more on the defensive as though you are about to invade thier Ni private space. When challenged you can see them get an eagle eye look as Te comes out. They can appear stiff, robotic, or very cold.
Speaking style can differ too. The entps are more give and take conversational, even if they are playing you a bit. The INTJs will be much more pedantic and tend to interrupt your attempts to cut them off. The INTJs are also much more dismissive if what you are saying is wrong. They will tell you outright. The entps likely think you are just as wrong but are a little better about letting you make an idiot of yourself and let you babble on, then cut you off with a smart ass remark. When you are on better terms most entps will actively engage you in debate, where the intjs really still act like you are arguing with them, even if you have known them for years.
INTJs can have a really sweet fragile soft spot if you can pull it out.
The entps want to have sex with you but the intjs usually just want to be friends, unless they want to marry you (or they are Edgar).