let's take for instance now, I a big dip occured in bitcoin, and you are yet to be paid from your work place, and you really don't want to miss out buying that dip, buddy there is nothing bad in collecting loan to invest in bitcoin, to buy that dip and hold provided you have a source
Taking a loan to leverage on an opportunity is not a bad idea if you have other means of paying it back, but in the scenario you explained here, it is a bad move and a loan you shouldn't be taking because this is your salary buddy, not your discretionary income, because I am sure that it's from that your salary you will remove money for your basic needs and few other important bills, which you aren't even sure if their will be something left capable to payback the loan, so in this scenario you explained, taking a loan is a bad move because it's coming from lack and you are not 100% sure of having enough left to still sorts out yourself and pay off the loan.
And it's not only necessary for you to take loan only when it only has to with emergencies,
This is another problem waiting to happen, you are mandatory to have an emergency funds in place so as to protect your investment from any real life emergencies, but investing without putting it in place with the hopes of taking a loan to cover up for it is another bad move you really needs to avoid.