Because it's only OK to ask for a raise when the boss has the upper hand?
That would be the upper hand.
Before that, it's just a discussion.
This industry doesn't value engineering experience. It values breadth over depth. There are some exceptions. But the data are what they are.
Every day I go to work, the implied threat is that my company could assign all my work to someone cheaper--generally speaking, give 1/Nth of my work to each of my N co-workers, then advertise an open position if that puts the team over capacity--and abruptly end our work-for-pay relationship. Or maybe they allow a tester to jump up into development, and give them tester+1 pay instead of developer pay. If I meet with my manager with competing offer in hand, that may invert the status quo of the power balance for all of 15 minutes. How unnerving for them.
You always need the company more than the company needs you. That's a corollary to the whole point of having a company, which is to produce an entity separate from and greater than its constituent parts.
Personally, I'd just keep silent about the amount of the competing offer and ask for a raise. They can do their own calculations about how much they can afford to give, and if they can't match the competing offer without knowing what it is, I'd take it. Telling them what that offer is makes as much sense as divulging your salary history when seeking out competing offers, which is to say it does not make sense. Let companies do their own calculation regarding how much you are worth to them, instead of copying the answers off of each other.
Besides, that's exactly how they gauge what kind of wages to offer when they hire you -- from what others would accept in your place.
You don't fire your girlfriend in tough times, but your boss will fire you if he had to. It's a stricylty pay to play relationship.
Spouses are loyal back, businesses are not.
Not saying that you should be concerned about getting fired everyday. But if you don't create demonstrable value to your company over a longer period of time (a couple of years perhaps) don't expect to keep the job. Things are moving wayy too fast today.
Outside of my own direct experience, I can also recall many other co-workers' experiences where the companies I've worked for went above and beyond in their commitment to their employees. One time that meant making many extraordinary allowances for an employee suffering from a mental breakdown. At times it has meant extending the employment of someone who was looking for a life/career change, but the company kept on paying a salary until the employee found somewhere new to land - way beyond where the employment had any real benefit to the company. There are many others.
By all means, takes some precautions. By all means, stand up for yourself. By all means, make sure that you're being fairly compensated... but if you go into every relationship, personal or business, with your shields raised and phasers set to kill - you will reap what you sow.
I know that personal relationships aren't exactly the same as business relationships, but to pretend that they aren't somewhat analogous doesn't line up with my own experiences. I've had a lot of personal relationships in business. Almost every boss I've ever had has been my friend on some level and the same goes with a lot of people who've worked for me.
When you treat people with respect, consideration, and friendship in your work life - you'll be surprised at how often you get the same from them in return.
Getting independent information of your value isn't "guns blazing."
Going out and getting a job offer is a step beyond that.
Work is NOT like having a girlfriend. Like the other poster said, a better analogy is your relationship with a prostitute. But it's good you brought up this incorrect analogy, because I think it really shows the horribly wrong mentality that bosses have, because they believe this to be a good analogy even though it isn't.
I'm not showing up to work every day because I have any warm and fuzzy personal feelings for the people there (especially the management). I go to work because they give me a paycheck. That's it. It's no different than prostitution, except not quite as icky. If my girlfriend tells me she needs to spend less time with me for a little while because she's going to spend some time with her family for some family problem, or she's working on her own start-up business and needs to spend extra time on it to make it successful, etc., then sure. If, however, employer tells me they need to cut my pay in half because they're having money problems, I'm immediately going to look for a new job. I don't have any personal feelings for my employer, and I don't expect to grow old and retire with them either, and I also know that if they don't need me any more, I'll be out the door with a pink slip that day.
I think this analogy really shows how many employers think (wrongly) that employees should have some kind of loyalty to them, even though the employers rarely have any loyalty back to the employees.
The person to whom you're responding explicitly drew a distinction between discussing a raise with your boss vs going to your boss with another offer that you have secured.
I can see the importance of that distinction. To put the relationship in a different context: Imagine the difference between a girlfriend who says, "Hey, we need to discuss the amount of time you spend playing video games. I'd like you to pay more attention to me." vs "Hey, I don't like the amount of time you spend playing video games, so I've been talking to this new guy about being my boyfriend. Your move."