If you want to practice in a private lobby, you can "verify" the auto bhop yourself by hosting a local server with cheats enabled.
You are now locally "verified" to auto bhop. Warning: These commands will fail on official Valve servers because sv_cheats must be 0. left 4 dead 2 auto bunny hop verified
The L4D2 community is split. Here is the consensus: If you want to practice in a private
The golden rule: Look for the server's "!rules" command before bhopping. If auto bhop is disallowed, players will see you sliding across the map at lightspeed and votekick you. You are now locally "verified" to auto bhop
In a standard, unmodified lobby, bunny hopping is extremely difficult. The Source Engine’s sv_autobunnyhopping command is set to 0, meaning you must tap the space bar with millisecond precision (the "perfect frame" trick). Missing a single jump reduces your speed to a crawl.
This is where "auto bunny hop" comes in.