What does a proper crash/burn build look like?

[BCS]

I keep trying to make them and keep dying to the blue boss with the shield and the glowy ball things.

[malroth_returns]

Start with a good early game weapon you can later forget about like flak or salvo, Grab Hullbreaker and either Warp or Amp shield. For mods your #1 priority is hull stregnth and regeneration and juggernaut then shield recharge, efficiency and skirmish then mix in shield/armour/passive damage upgrades as they appear.

[Shaotian]

I find that you can actually just skip on shield and weapon upgrades. Just shoot things till level 6 or 7 and then get hullbreaker, all the hull strength tree, regeneration and rapid reconstruction. After that, all of adaptive armor is very good, and you can take rebuke too for the duration just never shoot.
That's about it, dead wake deals a lot of dmg and the candescence tree is nice but you should probably avoid purge so you can heal more from purification.

[Kal]

The shield boss is an absolute fun-wrecker. It completely hard counters some builds unless you put in some way to get it down. If you want to use crash damage, this boss requires you to either have secondary damage such as Deadly Wake or enough regeneration to outlast it.

Now as for crash/burn builds, there are a couple of ways you can do them. The hullbreaker variant was already mentioned, so let me give you two more options:

The Bumper Car. Grab a Viper Hull and go down the rapid reconstruction/regeneration route. Next, invest in hull strength/damage reduction/burning, round off with some convenience mods and Ataraxia.
Playstyle is easy, just bump into any enemy and the flames from your hull burn up everything in sight. It quickly escalates into silly levels and is a lot of fun.

The Ghost Fire. Grab a Stealth Ship and aim for Apotheosis. Grab everything that can burn. Halo Shields, Burn, Deadly Wake, Celestial Lance. You're not technically crashing, since you fly straight through enemies but it's very much a melee burn build. This one doesn't need Ataraxia, so round it off with anything you want.
By the time you've got a few mods in, you're looking at several thousand burn damage. It doesn't translate well into the post game, since it lacks screen clear.