Take an early direct flight BLR (Kempegowda) to BKK (Suvarnabhumi). Direct flights ~4 hours; arrive midday so you have the afternoon and the night. Book low-cost carriers or economy fares for best price.
Take the Airport Rail Link or a budget taxi to central Bangkok and check into a budget highly rated hostel like Lub d Silom (clean, social, great reviews) or The Yard Hostel; both have private rooms and dorms for low cost.
Stretch your legs, try cheap street food pad thai or grilled skewers in Khao San or nearby Rambuttri; a lively area to ease into Bangkok's vibe and plan the night.
RCA (Royal City Avenue) hosts budget-friendly big clubs popular with locals and tourists — Onyx and Route66 are good choices; Thonglor's Sing Sing is stylish if you prefer a cooler vibe. Clubs open ~9pm and stay active until 2–3am.
Choose a full-day zipline and canopy tour near Cha-Am/Chonburi (operators run 8:00–16:00) for adrenaline and canopy walks, or a 3–4 hour Muay Thai group training session in Bangkok for a high-energy local experience. Both are highly recommended for a bachelor trip.
Try a street food crawl in Soi 38 or head to Chinatown for inexpensive and excellent seafood and noodle stalls open into the evening; great atmosphere and cheap prices.
Start with budget-friendly rooftop bars (some have happy-hour deals; check dress code) then head to Thonglor or Ekkamai clubs (Sing Sing, BEAM) for a higher-end but still accessible party. Clubs typically open 9pm–2am.
Take a 30–40 minute speedboat to Koh Larn for snorkeling, beach time, and optional jet-ski or banana-boat rides. Boats run throughout the day; operators usually work 8:00–17:00.
Pattaya's Walking Street is the epicenter of party life: clubs, go-go bars and big crowds. Many venues open from ~10pm and go until 3–4am; great for a raucous bachelor night.
Have a final group dinner at a beloved budget Thai spot such as Thip Samai Pad Thai (if you haven’t already) or a night market with varied cheap options.