We all know first impressions are important.

How important? It depends on who you ask. While it’s commonly stated that one third of hiring managers know in the first 90 seconds of meeting you whether they’re going to hire you or not, another, more recent study, suggests that only 5% actually decide in the first minute, while about 50% of make their decision in the first 5 – 15 minutes, and a full 22.5% still haven’t made up their mind by the end of the interview and have to decide later.

Regardless of exact numbers, you certainly can blow your chances right off the bat – sometimes before you even open your mouth to answer the first question.

Here are eight ways to do that.

Posting something stupid online. Don’t post something like: “Job interview tomorrow. Time to look super eager for a job I don’t even want!” on Facebook. You think you’re safe because only your “friends” (500 people, 400 of whom you barely know) can see your posts. But if one of those “friends” turns out to be better friends with the hiring manager, you’re sunk. It’s also a bad idea to make any sort of comment or joke that could cause offense to, well, anyone anywhere ever.

Telling the hiring manager to eff off. Come on. That’s just crazy, right? You’d NEVER do that. Well, imagine you’re driving to the interview and someone cuts you off, so you give them the finger. Or you’re on the subway and you tell a guy who gets in your way to go eff himself — and then you get to your interview and … guess who the interviewer is! That second scenario actually happened. Be nice.

Showing up late. I am late to everything, literally everything. Except job interviews (mostly). Being late for the interview sends the message that you don’t give a damn. Be on time. (And if you’re chronically late for everything in life make sure you make up for it in other ways.)

Offering a bad handshake. Bad handshakes can be weird at best, gross at worst. Grip firmly but not too firmly, don’t be sweaty, don’t be too perfunctory or hold on too long. And for the sake of everything that is good and holy, wash your hands beforehand. A hiring manager once told me about seeing someone come out of a men’s room stall and leave without washing his hands. The guy turned out to be his next interview. “I told him I had arthritis, and couldn’t shake hands,” he said. The guy did not get the job. Because, ew.

Not looking the part. Most people know to dress professionally and be well groomed for the interview. But appropriate dress actually depends on the industry and company. Do some research and find out what to wear in order to fit in with the company culture. A law firm probably requires a suit, while a suit might be too much for some ad agencies. Ask friends, look at the corporate website, check out the social media accounts of the company and of employees. (More about what to wear to the interview by industry here.)

Smelling bad. Bad breath, body odor, reeking of smoke – all turn offs. Brush your teeth, visit the dentist, chew gum (but spit it out before you go in), use mouthwash. Don’t smoke before the interview. Shower, use deodorant. Don’t overload on the perfume.

Carrying or wearing a rival company’s product. Don’t bring your iPad to an interview at Microsoft. This Wall Street Journal article contains a story about someone who showed up for an interview at PepsiCo with a bottle of Dasani water. Dasani is a Coke product. He didn’t get the job.

Bringing something else that puts your judgment or intelligence into question. A copy of Fifty Shades of Grey perhaps, or a celebrity gossip mag. Unless the interview is for a job at said gossip mag, leave the lowbrow reading material at home. (See a whole list of things not to bring to the interview here.)