First most people don’t understand how and what makes a Jew, and what it required by Halkalah, or Jewish Law.
Most people associate Jews dressed in black with sidelocks as Orthodox Jews, the reality is they are members of several groups of Ultra Orthodox Jews who derived from a movement called Chabad, or Chabad Lubavich. The Chabad Lubavich movement is about 175 years old, and was a reaction to the development of Reform and Conservative Judaism. The Chabad movement became so excessive, and so anti-social not wanting to deal with other Jews or Gentiles, and took such a strict interpretation not only of the Torah, but other writings that they were eventually excommunicated from mainline Judaism. In Judaism it is very hard to get oneself or group excommunicated.
Most Orthodox Jews you meet will not have the Peis, or sidelocks. They will wear a kippah, or yalmuka, or another headcovering, anything from a baseball cap to fedora. Many will wear a small prayer shawl under the clothes with titzis, or fringes. They will otherwise wear modest clothing that follows the current fashion. They don’t for the most part interpret the same passage about not rounding the corners of your head as meaning sidelocks. Many not all do not wear beards. You may not know they are Orthodox by looking at them.
Conservative and Reformed Jews interpret the implementation of the Law differently but are accepted by all other Jews as being 100% Jewish.
As Catholics and Orthodox, we sin if we eat meat on a day it is proscribed, unless there is a serious reason to do so, (health, danger of starvation, compelled to by threat to our lives.) Jews interpret the idea of following the Mitzvot, (Good actions or deeds) diffenently that Christians do. While we translate Mitzvot, as Law, Jews would say that God has listed for us the Ten Commandments, which are a summary of the most important things we must avoid, and the rest of the Mitzot in the Torah are things that we gain merit from either avoiding or doing. So to avoid pork is a good deed, to eat it is not held to be sinful in the same way as a Catholic who eats meat on a Friday in Lent. To keep Sabbath observances will make you holier, to not will not always make you worse. So a Jew would be encouraged to preform one additional good action or deed every day, but would not be rejected as a Jew if he did not preform all of them. The only real reason for being expelled or excommunicated is to set bad examples, and call yourself an observant Jew.
One case is that of Baruch Spinoza, a philosoper who’s ideas included speculation about Pantheism and Athiesm. The Ban included the following, [b:kyi1mdit][i:kyi1mdit]”The chiefs of the council make known to you that having long known of evil opinions and acts of Baruch de Spinoza, they have endeavored by various means and promises to turn him from evil ways. Not being able to find any remedy, but on the contrary receiving every day more information about the abominable heresies practiced and taught by him, and about the monstrous acts committed by him, having this from many trustworthy witnesses who have deposed and borne witness on all this in the presence of said Spinoza, who has been convicted; all this having been examined in the presence of the Rabbis, the council decided, with the advice of the Rabbi, that the said Spinoza should be excommunicated and cut off from the Nation of Israel.”[/i:kyi1mdit][/b:kyi1mdit]
So to a Jew, your behavior as a whole is more important than how many of the Mitzvot you practice.