[raverbashing]

This phrase probably uses the verb kontrollieren, which means check/control/examine

It's not about petty bureaucrats and trivial infractions, it usually is referring to someone getting checked on the subway for tickets - and sometimes not having the proper ticket (or maaaaaybe being asked for id due to anti-social behaviour)

[C1sc0cat]

Or being one of those "brown" Germans

[raverbashing]

Are you talking from experience?

On the u-bahn everybody is checked. As for anti-social behaviour, it's usually the ones with certain clothing, possibly depicting some symbols or personal appearance that are often targeted.