Bam slam has many meanings, all of which are great. It is a common exclamation similar to "Great!" and "Awesome!" And also shares close relations to phrases like "sucks to suck!" It is definitely a trending thing. Anyone who says it is bound to be deemed the cool one in their society.
"Whoa! You just won the lottery!"
"Bam slam!"
"Damnit Maurice! Why'd you do that?"
*shrugs* "Bam slam!"
"BAM. SLAM."
"Wow, Kurtain, you did amazing on that test!"
"Bam Slam!"
"You went skydiving?! That's some Bam Slammery right there."